Spatially variable liquid crystal diffraction gratings

ABSTRACT

The present disclosure relates to display systems and, more particularly, to augmented reality display systems. A diffraction grating includes a plurality of different diffracting zones having a periodically repeating lateral dimension corresponding to a grating period adapted for light diffraction. The diffraction grating additionally includes a plurality of different liquid crystal layers corresponding to the different diffracting zones. The different liquid crystal layers have liquid crystal molecules that are aligned differently, such that the different diffracting zones have different optical properties associated with light diffraction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/424,310, filed Nov. 18, 2016, entitled“SPATIALLY VARIABLE LIQUID CRYSTAL DIFFRACTION GRATINGS,” the content ofwhich is hereby incorporated by reference herein in its entirety.

BACKGROUND Field

The present disclosure relates to display systems and, moreparticularly, to augmented reality display systems.

Description of the Related Art

Modern computing and display technologies have facilitated thedevelopment of systems for so called “virtual reality” or “augmentedreality” experiences, wherein digitally reproduced images or portionsthereof are presented to a user in a manner wherein they seem to be, ormay be perceived as, real. A virtual reality, or “VR”, scenariotypically involves presentation of digital or virtual image informationwithout transparency to other actual real-world visual input; anaugmented reality, or “AR”, scenario typically involves presentation ofdigital or virtual image information as an augmentation to visualizationof the actual world around the user. A mixed reality, or “MR”, scenariois a type of AR scenario and typically involves virtual objects that areintegrated into, and responsive to, the natural world. For example, inan MR scenario, AR image content may be blocked by or otherwise beperceived as interacting with objects in the real world.

Referring to FIG. 1, an augmented reality scene 1 is depicted wherein auser of an AR technology sees a real-world park-like setting 1100featuring people, trees, buildings in the background, and a concreteplatform 1120. In addition to these items, the user of the AR technologyalso perceives that he “sees” “virtual content” such as a robot statue1110 standing upon the real-world platform 1120, and a cartoon-likeavatar character 1130 flying by which seems to be a personification of abumble bee, even though these elements 1130, 1110 do not exist in thereal world. Because the human visual perception system is complex, it ischallenging to produce an AR technology that facilitates a comfortable,natural-feeling, rich presentation of virtual image elements amongstother virtual or real-world imagery elements.

Systems and methods disclosed herein address various challenges relatedto AR and VR technology.

SUMMARY

Accordingly, numerous devices, systems, structures and methods aredisclosed herein. For instance, an example diffraction grating isdisclosed that includes a plurality of different diffracting zoneshaving a periodically repeating lateral dimension corresponding to agrating period adapted for light diffraction. The diffraction gratingadditionally includes a plurality of different liquid crystal layerscorresponding to the different diffracting zones. The different liquidcrystal layers have liquid crystal molecules that are aligneddifferently, such that the different diffracting zones have differentoptical properties associated with light diffraction.

An example method of fabricating a diffraction grating is disclosed thatincludes providing a substrate and providing a plurality of differentdiffracting zones on the substrate having a periodically repeatinglateral dimension corresponding to a grating period adapted for lightdiffraction. The method further includes forming a plurality ofdifferent liquid crystal layers comprising liquid crystal molecules overthe substrate, the different liquid crystal layers corresponding to thedifferent diffracting zones, wherein forming the different liquidcrystal layers comprises aligning the liquid crystal moleculesdifferently, thereby providing different optical properties associatedwith light diffraction to the different diffracting zones.

Another example diffraction grating is disclosed that includes aplurality of contiguous liquid crystal layers extending in a lateraldirection and arranged to have a periodically repeating lateraldimension, a thickness and indices of refraction such that the liquidcrystal layers are configured to diffract light. Liquid crystalmolecules of the liquid crystal layers are arranged differently indifferent liquid crystal layers along the lateral direction such thatthe contiguous liquid crystal layers are configured to diffract lightwith a gradient in diffraction efficiency.

An example head-mounted display device that is configured to projectlight to an eye of a user to display augmented reality image content isalso disclosed. The head-mounted display device includes a frameconfigured to be supported on a head of the user. The head-mounteddisplay device additionally includes a display disposed on the frame, atleast a portion of said display comprising one or more waveguides, saidone or more waveguides being transparent and disposed at a location infront of the user's eye when the user wears said head-mounted displaydevice such that said transparent portion transmits light from a portionof an environment in front of the user to the user's eye to provide aview of said portion of the environment in front of the user, saiddisplay further comprising one or more light sources and at least onediffraction grating configured to couple light from the light sourcesinto said one or more waveguides or to couple light out of said one ormore waveguides. The diffraction grating includes a plurality ofdifferent diffracting zones having a periodically repeating lateraldimension corresponding to a grating period adapted for lightdiffraction. The diffraction grating additionally includes a pluralityof different liquid crystal layers corresponding to the differentdiffracting zones, wherein the different liquid crystal layers haveliquid crystal molecules that are aligned differently, such that thedifferent diffracting zones have different optical properties associatedwith light diffraction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a user's view of augmented reality (AR) through an ARdevice.

FIG. 2 illustrates an example of wearable display system.

FIG. 3 illustrates a conventional display system for simulatingthree-dimensional imagery for a user.

FIG. 4 illustrates aspects of an approach for simulatingthree-dimensional imagery using multiple depth planes.

FIGS. 5A-5C illustrate relationships between radius of curvature andfocal radius.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user.

FIG. 7 illustrates an example of exit beams outputted by a waveguide.

FIG. 8 illustrates an example of a stacked waveguide assembly in whicheach depth plane includes images formed using multiple differentcomponent colors.

FIG. 9A illustrates a cross-sectional side view of an example of a setof stacked waveguides that each includes an incoupling optical element.

FIG. 9B illustrates a perspective view of an example of the plurality ofstacked waveguides of FIG. 9A.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B.

FIGS. 10A-10C illustrate cross-sectional side views of diffractiongratings having zones in which liquid crystal molecules have differentpre-tilt angles, according to embodiments.

FIGS. 11A-11B are cross-sectional side views of an intermediatestructure and a diffraction grating illustrating a method of fabricatingthe diffraction gratings illustrated in FIGS. 10A-10C, according toembodiments.

FIGS. 12A-12C are cross-sectional side views of intermediate structuresand a diffraction grating illustrating a method of fabricating thediffraction gratings illustrated in FIGS. 10A-10C, according toembodiments.

FIGS. 13A-13B illustrate cross-sectional side views of diffractiongratings having zones in which liquid crystal molecules have differentpre-tilt angles, according to embodiments.

FIGS. 14A-14B are cross-sectional side views of an intermediatestructure and a diffraction grating illustrating a method of fabricatingthe diffraction gratings illustrated in FIGS. 13A-13B, according toembodiments.

FIGS. 15A-15C illustrate top down plan views of diffraction gratingshaving zones in which liquid crystal molecules have different azimuthalangles, according to embodiments.

FIG. 16A illustrates a top down plan view of a diffraction gratinghaving zones in which liquid crystal molecules have different azimuthalangles, according to embodiments.

FIG. 16B is a schematic graph illustrating variations in azimuthalangles in a lateral direction across different zones of the diffractiongrating illustrated in FIG. 16A.

FIGS. 17A-17D illustrate cross-sectional side views of intermediatestructures and a diffraction gratings illustrating a method offabricating the diffraction gratings illustrated in FIGS. 15A-15C,according to embodiments.

FIG. 17E illustrates a top down plan view of the diffraction gratingillustrated in FIG. 17D, according to embodiments.

FIGS. 18A-18C illustrate cross-sectional side views of intermediatestructures and a diffraction gratings illustrating a method offabricating the diffraction gratings illustrated in FIG. 16A, accordingto embodiments.

FIG. 18D illustrates a top down plan view of the diffraction gratingillustrated in FIG. 18C, according to embodiments.

FIGS. 19A-19B illustrate top down and cross-sectional side views of adiffraction grating having zones in which liquid crystal molecules havedifferent chirality, according to embodiments.

FIG. 20 is a cross-sectional side view of a diffraction grating havingzones in which liquid crystal molecules have different chirality,according to embodiments.

FIG. 21 is a cross-sectional side view of a diffraction grating havingzones in which liquid crystal layers are formed of different liquidcrystal materials, according to embodiments.

DETAILED DESCRIPTION

AR systems may display virtual content to a user, or viewer, while stillallowing the user to see the world around them. Preferably, this contentis displayed on a head-mounted display, e.g., as part of eyewear, thatprojects image information to the user's eyes. In addition, the displaymay also transmit light from the surrounding environment to the user'seyes, to allow a view of that surrounding environment. As used herein,it will be appreciated that a “head-mounted” display is a display thatmay be mounted on the head of a viewer.

Reference will now be made to the drawings, in which like referencenumerals refer to like parts throughout.

FIG. 2 illustrates an example of wearable display system 80. The displaysystem 80 includes a display 62, and various mechanical and electronicmodules and systems to support the functioning of that display 62. Thedisplay 62 may be coupled to a frame 64, which is wearable by a displaysystem user or viewer 60 and which is configured to position the display62 in front of the eyes of the user 60. The display 62 may be consideredeyewear in some embodiments. In some embodiments, a speaker 66 iscoupled to the frame 64 and positioned adjacent the ear canal of theuser 60 (in some embodiments, another speaker, not shown, is positionedadjacent the other ear canal of the user to provide for stereo/shapeablesound control). In some embodiments, the display system may also includeone or more microphones 67 or other devices to detect sound. In someembodiments, the microphone is configured to allow the user to provideinputs or commands to the system 80 (e.g., the selection of voice menucommands, natural language questions, etc.), and/or may allow audiocommunication with other persons (e.g., with other users of similardisplay systems The microphone may further be configured as a peripheralsensor to continuously collect audio data (e.g., to passively collectfrom the user and/or environment). Such audio data may include usersounds such as heavy breathing, or environmental sounds, such as a loudbang indicative of a nearby event. The display system may also include aperipheral sensor 30 a, which may be separate from the frame 64 andattached to the body of the user 60 (e.g., on the head, torso, anextremity, etc. of the user 60). The peripheral sensor 30 a may beconfigured to acquire data characterizing the physiological state of theuser 60 in some embodiments, as described further herein. For example,the sensor 30 a may be an electrode.

With continued reference to FIG. 2, the display 62 is operativelycoupled by communications link 68, such as by a wired lead or wirelessconnectivity, to a local data processing module 70 which may be mountedin a variety of configurations, such as fixedly attached to the frame64, fixedly attached to a helmet or hat worn by the user, embedded inheadphones, or otherwise removably attached to the user 60 (e.g., in abackpack-style configuration, in a belt-coupling style configuration).Similarly, the sensor 30 a may be operatively coupled by communicationslink 30 b, e.g., a wired lead or wireless connectivity, to the localprocessor and data module 70. The local processing and data module 70may comprise a hardware processor, as well as digital memory, such asnon-volatile memory (e.g., flash memory or hard disk drives), both ofwhich may be utilized to assist in the processing, caching, and storageof data. The data include data a) captured from sensors (which may be,e.g., operatively coupled to the frame 64 or otherwise attached to theuser 60), such as image capture devices (such as cameras), microphones,inertial measurement units, accelerometers, compasses, GPS units, radiodevices, gyros, and/or other sensors disclosed herein; and/or b)acquired and/or processed using remote processing module 72 and/orremote data repository 74 (including data relating to virtual content),possibly for passage to the display 62 after such processing orretrieval. The local processing and data module 70 may be operativelycoupled by communication links 76, 78, such as via a wired or wirelesscommunication links, to the remote processing module 72 and remote datarepository 74 such that these remote modules 72, 74 are operativelycoupled to each other and available as resources to the local processingand data module 70. In some embodiments, the local processing and datamodule 70 may include one or more of the image capture devices,microphones, inertial measurement units, accelerometers, compasses, GPSunits, radio devices, and/or gyros. In some other embodiments, one ormore of these sensors may be attached to the frame 64, or may bestandalone structures that communicate with the local processing anddata module 70 by wired or wireless communication pathways.

With continued reference to FIG. 2, in some embodiments, the remoteprocessing module 72 may comprise one or more processors configured toanalyze and process data and/or image information. In some embodiments,the remote data repository 74 may comprise a digital data storagefacility, which may be available through the internet or othernetworking configuration in a “cloud” resource configuration. In someembodiments, the remote data repository 74 may include one or moreremote servers, which provide information, e.g., information forgenerating augmented reality content, to the local processing and datamodule 70 and/or the remote processing module 72. In some embodiments,all data is stored and all computations are performed in the localprocessing and data module, allowing fully autonomous use from a remotemodule.

The perception of an image as being “three-dimensional” or “3-D” may beachieved by providing slightly different presentations of the image toeach eye of the viewer. FIG. 3 illustrates a conventional display systemfor simulating three-dimensional imagery for a user. Two distinct images5, 7—one for each eye 4, 6—are outputted to the user. The images 5, 7are spaced from the eyes 4, 6 by a distance 10 along an optical orz-axis parallel to the line of sight of the viewer. The images 5, 7 areflat and the eyes 4, 6 may focus on the images by assuming a singleaccommodated state. Such systems rely on the human visual system tocombine the images 5, 7 to provide a perception of depth and/or scalefor the combined image.

It will be appreciated, however, that the human visual system is morecomplicated and providing a realistic perception of depth is morechallenging. For example, many viewers of conventional “3-D” displaysystems find such systems to be uncomfortable or may not perceive asense of depth at all. Without being limited by theory, it is believedthat viewers of an object may perceive the object as being“three-dimensional” due to a combination of vergence and accommodation.Vergence movements (i.e., rotation of the eyes so that the pupils movetoward or away from each other to converge the lines of sight of theeyes to fixate upon an object) of the two eyes relative to each otherare closely associated with focusing (or “accommodation”) of the lensesand pupils of the eyes. Under normal conditions, changing the focus ofthe lenses of the eyes, or accommodating the eyes, to change focus fromone object to another object at a different distance will automaticallycause a matching change in vergence to the same distance, under arelationship known as the “accommodation-vergence reflex,” as well aspupil dilation or constriction. Likewise, a change in vergence willtrigger a matching change in accommodation of lens shape and pupil size,under normal conditions. As noted herein, many stereoscopic or “3-D”display systems display a scene using slightly different presentations(and, so, slightly different images) to each eye such that athree-dimensional perspective is perceived by the human visual system.Such systems are uncomfortable for many viewers, however, since they,among other things, simply provide a different presentation of a scene,but with the eyes viewing all the image information at a singleaccommodated state, and work against the “accommodation-vergencereflex.” Display systems that provide a better match betweenaccommodation and vergence may form more realistic and comfortablesimulations of three-dimensional imagery contributing to increasedduration of wear and in turn compliance to diagnostic and therapyprotocols.

FIG. 4 illustrates aspects of an approach for simulatingthree-dimensional imagery using multiple depth planes. With reference toFIG. 4, objects at various distances from eyes 4, 6 on the z-axis areaccommodated by the eyes 4, 6 so that those objects are in focus. Theeyes (4 and 6) assume particular accommodated states to bring into focusobjects at different distances along the z-axis. Consequently, aparticular accommodated state may be said to be associated with aparticular one of depth planes 14, with has an associated focaldistance, such that objects or parts of objects in a particular depthplane are in focus when the eye is in the accommodated state for thatdepth plane. In some embodiments, three-dimensional imagery may besimulated by providing different presentations of an image for each ofthe eyes 4, 6, and also by providing different presentations of theimage corresponding to each of the depth planes. While shown as beingseparate for clarity of illustration, it will be appreciated that thefields of view of the eyes 4, 6 may overlap, for example, as distancealong the z-axis increases. In addition, while shown as flat for ease ofillustration, it will be appreciated that the contours of a depth planemay be curved in physical space, such that all features in a depth planeare in focus with the eye in a particular accommodated state.

The distance between an object and the eye 4 or 6 may also change theamount of divergence of light from that object, as viewed by that eye.FIGS. 5A-5C illustrates relationships between distance and thedivergence of light rays. The distance between the object and the eye 4is represented by, in order of decreasing distance, R1, R2, and R3. Asshown in FIGS. 5A-5C, the light rays become more divergent as distanceto the object decreases. As distance increases, the light rays becomemore collimated. Stated another way, it may be said that the light fieldproduced by a point (the object or a part of the object) has a sphericalwavefront curvature, which is a function of how far away the point isfrom the eye of the user. The curvature increases with decreasingdistance between the object and the eye 4. Consequently, at differentdepth planes, the degree of divergence of light rays is also different,with the degree of divergence increasing with decreasing distancebetween depth planes and the viewer's eye 4. While only a single eye 4is illustrated for clarity of illustration in FIGS. 5A-5C and otherfigures herein, it will be appreciated that the discussions regardingeye 4 may be applied to both eyes 4 and 6 of a viewer.

Without being limited by theory, it is believed that the human eyetypically can interpret a finite number of depth planes to provide depthperception. Consequently, a highly believable simulation of perceiveddepth may be achieved by providing, to the eye, different presentationsof an image corresponding to each of these limited number of depthplanes. The different presentations may be separately focused by theviewer's eyes, thereby helping to provide the user with depth cues basedon the accommodation of the eye required to bring into focus differentimage features for the scene located on different depth plane and/orbased on observing different image features on different depth planesbeing out of focus.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user. A display system 1000 includes a stack ofwaveguides, or stacked waveguide assembly, 1178 that may be utilized toprovide three-dimensional perception to the eye/brain using a pluralityof waveguides 1182, 1184, 1186, 1188, 1190. In some embodiments, thedisplay system 1000 is the system 80 of FIG. 2, with FIG. 6schematically showing some parts of that system 80 in greater detail.For example, the waveguide assembly 1178 may be part of the display 62of FIG. 2. It will be appreciated that the display system 1000 may beconsidered a light field display in some embodiments.

With continued reference to FIG. 6, the waveguide assembly 1178 may alsoinclude a plurality of features 1198, 1196, 1194, 1192 between thewaveguides. In some embodiments, the features 1198, 1196, 1194, 1192 maybe one or more lenses. The waveguides 1182, 1184, 1186, 1188, 1190and/or the plurality of lenses 1198, 1196, 1194, 1192 may be configuredto send image information to the eye with various levels of wavefrontcurvature or light ray divergence. Each waveguide level may beassociated with a particular depth plane and may be configured to outputimage information corresponding to that depth plane. Image injectiondevices 1200, 1202, 1204, 1206, 1208 may function as a source of lightfor the waveguides and may be utilized to inject image information intothe waveguides 1182, 1184, 1186, 1188, 1190, each of which may beconfigured, as described herein, to distribute incoming light acrosseach respective waveguide, for output toward the eye 4. Light exits anoutput surface 1300, 1302, 1304, 1306, 1308 of the image injectiondevices 1200, 1202, 1204, 1206, 1208 and is injected into acorresponding input surface 1382, 1384, 1386, 1388, 1390 of thewaveguides 1182, 1184, 1186, 1188, 1190. In some embodiments, the eachof the input surfaces 1382, 1384, 1386, 1388, 1390 may be an edge of acorresponding waveguide, or may be part of a major surface of thecorresponding waveguide (that is, one of the waveguide surfaces directlyfacing the world 1144 or the viewer's eye 4). In some embodiments, asingle beam of light (e.g. a collimated beam) may be injected into eachwaveguide to output an entire field of cloned collimated beams that aredirected toward the eye 4 at particular angles (and amounts ofdivergence) corresponding to the depth plane associated with aparticular waveguide. In some embodiments, a single one of the imageinjection devices 1200, 1202, 1204, 1206, 1208 may be associated withand inject light into a plurality (e.g., three) of the waveguides 1182,1184, 1186, 1188, 1190.

In some embodiments, the image injection devices 1200, 1202, 1204, 1206,1208 are discrete displays that each produce image information forinjection into a corresponding waveguide 1182, 1184, 1186, 1188, 1190,respectively. In some other embodiments, the image injection devices1200, 1202, 1204, 1206, 1208 are the output ends of a single multiplexeddisplay which may, e.g., pipe image information via one or more opticalconduits (such as fiber optic cables) to each of the image injectiondevices 1200, 1202, 1204, 1206, 1208. It will be appreciated that theimage information provided by the image injection devices 1200, 1202,1204, 1206, 1208 may include light of different wavelengths, or colors(e.g., different component colors, as discussed herein).

In some embodiments, the light injected into the waveguides 1182, 1184,1186, 1188, 1190 is provided by a light projector system 2000, whichcomprises a light module 2040, which may include a light emitter, suchas a light emitting diode (LED). The light from the light module 2040may be directed to and modified by a light modulator 2030, e.g., aspatial light modulator, via a beam splitter 2050. The light modulator2030 may be configured to change the perceived intensity of the lightinjected into the waveguides 1182, 1184, 1186, 1188, 1190. Examples ofspatial light modulators include liquid crystal displays (LCD) includinga liquid crystal on silicon (LCOS) displays.

In some embodiments, the display system 1000 may be a scanning fiberdisplay comprising one or more scanning fibers configured to projectlight in various patterns (e.g., raster scan, spiral scan, Lissajouspatterns, etc.) into one or more waveguides 1182, 1184, 1186, 1188, 1190and ultimately to the eye 4 of the viewer. In some embodiments, theillustrated image injection devices 1200, 1202, 1204, 1206, 1208 mayschematically represent a single scanning fiber or a bundles of scanningfibers configured to inject light into one or a plurality of thewaveguides 1182, 1184, 1186, 1188, 1190. In some other embodiments, theillustrated image injection devices 1200, 1202, 1204, 1206, 1208 mayschematically represent a plurality of scanning fibers or a plurality ofbundles of scanning, fibers each of which are configured to inject lightinto an associated one of the waveguides 1182, 1184, 1186, 1188, 1190.It will be appreciated that the one or more optical fibers may beconfigured to transmit light from the light module 2040 to the one ormore waveguides 1182, 1184, 1186, 1188, 1190. It will be appreciatedthat one or more intervening optical structures may be provided betweenthe scanning fiber, or fibers, and the one or more waveguides 1182,1184, 1186, 1188, 1190 to, e.g., redirect light exiting the scanningfiber into the one or more waveguides 1182, 1184, 1186, 1188, 1190.

A controller 1210 controls the operation of one or more of the stackedwaveguide assembly 1178, including operation of the image injectiondevices 1200, 1202, 1204, 1206, 1208, the light source 2040, and thelight modulator 2030. In some embodiments, the controller 1210 is partof the local data processing module 70. The controller 1210 includesprogramming (e.g., instructions in a non-transitory medium) thatregulates the timing and provision of image information to thewaveguides 1182, 1184, 1186, 1188, 1190 according to, e.g., any of thevarious schemes disclosed herein. In some embodiments, the controllermay be a single integral device, or a distributed system connected bywired or wireless communication channels. The controller 1210 may bepart of the processing modules 70 or 72 (FIG. 1) in some embodiments.

With continued reference to FIG. 6, the waveguides 1182, 1184, 1186,1188, 1190 may be configured to propagate light within each respectivewaveguide by total internal reflection (TIR). The waveguides 1182, 1184,1186, 1188, 1190 may each be planar or have another shape (e.g.,curved), with major top and bottom surfaces and edges extending betweenthose major top and bottom surfaces. In the illustrated configuration,the waveguides 1182, 1184, 1186, 1188, 1190 may each include outcouplingoptical elements 1282, 1284, 1286, 1288, 1290 that are configured toextract light out of a waveguide by redirecting the light, propagatingwithin each respective waveguide, out of the waveguide to output imageinformation to the eye 4. Extracted light may also be referred to asoutcoupled light and the outcoupling optical elements light may also bereferred to light extracting optical elements. An extracted beam oflight is outputted by the waveguide at locations at which the lightpropagating in the waveguide strikes a light extracting optical element.The outcoupling optical elements 1282, 1284, 1286, 1288, 1290 may, forexample, be gratings, including diffractive optical features, asdiscussed further herein. While illustrated disposed at the bottom majorsurfaces of the waveguides 1182, 1184, 1186, 1188, 1190 for ease ofdescription and drawing clarity, in some embodiments, the outcouplingoptical elements 1282, 1284, 1286, 1288, 1290 may be disposed at the topand/or bottom major surfaces, and/or may be disposed directly in thevolume of the waveguides 1182, 1184, 1186, 1188, 1190, as discussedfurther herein. In some embodiments, the outcoupling optical elements1282, 1284, 1286, 1288, 1290 may be formed in a layer of material thatis attached to a transparent substrate to form the waveguides 1182,1184, 1186, 1188, 1190. In some other embodiments, the waveguides 1182,1184, 1186, 1188, 1190 may be a monolithic piece of material and theoutcoupling optical elements 1282, 1284, 1286, 1288, 1290 may be formedon a surface and/or in the interior of that piece of material.

With continued reference to FIG. 6, as discussed herein, each waveguide1182, 1184, 1186, 1188, 1190 is configured to output light to form animage corresponding to a particular depth plane. For example, thewaveguide 1182 nearest the eye may be configured to deliver collimatedlight, as injected into such waveguide 1182, to the eye 4. Thecollimated light may be representative of the optical infinity focalplane. The next waveguide up 1184 may be configured to send outcollimated light which passes through the first lens 1192 (e.g., anegative lens) before it can reach the eye 4; such first lens 1192 maybe configured to create a slight convex wavefront curvature so that theeye/brain interprets light coming from that next waveguide up 1184 ascoming from a first focal plane closer inward toward the eye 4 fromoptical infinity. Similarly, the third up waveguide 1186 passes itsoutput light through both the first 1192 and second 1194 lenses beforereaching the eye 4; the combined optical power of the first 1192 andsecond 1194 lenses may be configured to create another incrementalamount of wavefront curvature so that the eye/brain interprets lightcoming from the third waveguide 1186 as coming from a second focal planethat is even closer inward toward the person from optical infinity thanwas light from the next waveguide up 1184.

The other waveguide layers 1188, 1190 and lenses 1196, 1198 aresimilarly configured, with the highest waveguide 1190 in the stacksending its output through all of the lenses between it and the eye foran aggregate focal power representative of the closest focal plane tothe person. To compensate for the stack of lenses 1198, 1196, 1194, 1192when viewing/interpreting light coming from the world 1144 on the otherside of the stacked waveguide assembly 1178, a compensating lens layer1180 may be disposed at the top of the stack to compensate for theaggregate power of the lens stack 1198, 1196, 1194, 1192 below. Such aconfiguration provides as many perceived focal planes as there areavailable waveguide/lens pairings. Both the outcoupling optical elementsof the waveguides and the focusing aspects of the lenses may be static(i.e., not dynamic or electro-active). In some alternative embodiments,either or both may be dynamic using electro-active features.

In some embodiments, two or more of the waveguides 1182, 1184, 1186,1188, 1190 may have the same associated depth plane. For example,multiple waveguides 1182, 1184, 1186, 1188, 1190 may be configured tooutput images set to the same depth plane, or multiple subsets of thewaveguides 1182, 1184, 1186, 1188, 1190 may be configured to outputimages set to the same plurality of depth planes, with one set for eachdepth plane. This can provide advantages for forming a tiled image toprovide an expanded field of view at those depth planes.

With continued reference to FIG. 6, the outcoupling optical elements1282, 1284, 1286, 1288, 1290 may be configured to both redirect lightout of their respective waveguides and to output this light with theappropriate amount of divergence or collimation for a particular depthplane associated with the waveguide. As a result, waveguides havingdifferent associated depth planes may have different configurations ofoutcoupling optical elements 1282, 1284, 1286, 1288, 1290, which outputlight with a different amount of divergence depending on the associateddepth plane. In some embodiments, the light extracting optical elements1282, 1284, 1286, 1288, 1290 may be volumetric or surface features,which may be configured to output light at specific angles. For example,the light extracting optical elements 1282, 1284, 1286, 1288, 1290 maybe volume holograms, surface holograms, and/or diffraction gratings. Insome embodiments, the features 1198, 1196, 1194, 1192 may not be lenses;rather, they may simply be spacers (e.g., cladding layers and/orstructures for forming air gaps).

In some embodiments, the outcoupling optical elements 1282, 1284, 1286,1288, 1290 are diffractive features that form a diffraction pattern, or“diffractive optical element” (also referred to herein as a “DOE”).Preferably, the DOE's have a sufficiently low diffraction efficiency sothat only a portion of the light of the beam is deflected away towardthe eye 4 with each intersection of the DOE, while the rest continues tomove through a waveguide via total internal reflection. The lightcarrying the image information is thus divided into a number of relatedexit beams that exit the waveguide at a multiplicity of locations andthe result is a fairly uniform pattern of exit emission toward the eye 4for this particular collimated beam bouncing around within a waveguide.

In some embodiments, one or more DOEs may be switchable between “on”states in which they actively diffract, and “off” states in which theydo not significantly diffract. For instance, a switchable DOE maycomprise a layer of polymer dispersed liquid crystal, in whichmicrodroplets comprise a diffraction pattern in a host medium, and therefractive index of the microdroplets may be switched to substantiallymatch the refractive index of the host material (in which case thepattern does not appreciably diffract incident light) or themicrodroplet may be switched to an index that does not match that of thehost medium (in which case the pattern actively diffracts incidentlight).

In some embodiments, a camera assembly 500 (e.g., a digital camera,including visible light and infrared light cameras) may be provided tocapture images of the eye 4 and/or tissue around the eye 4 to, e.g.,detect user inputs and/or to monitor the physiological state of theuser. As used herein, a camera may be any image capture device. In someembodiments, the camera assembly 500 may include an image capture deviceand a light source to project light (e.g., infrared light) to the eye,which may then be reflected by the eye and detected by the image capturedevice. In some embodiments, the camera assembly 500 may be attached tothe frame 64 (FIG. 2) and may be in electrical communication with theprocessing modules 70 and/or 72, which may process image informationfrom the camera assembly 500 to make various determinations regarding,e.g., the physiological state of the user, as discussed herein. It willbe appreciated that information regarding the physiological state ofuser may be used to determine the behavioral or emotional state of theuser. Examples of such information include movements of the user and/orfacial expressions of the user. The behavioral or emotional state of theuser may then be triangulated with collected environmental and/orvirtual content data so as to determine relationships between thebehavioral or emotional state, physiological state, and environmental orvirtual content data. In some embodiments, one camera assembly 500 maybe utilized for each eye, to separately monitor each eye.

With reference now to FIG. 7, an example of exit beams outputted by awaveguide is shown. One waveguide is illustrated, but it will beappreciated that other waveguides in the waveguide assembly 1178 (FIG.6) may function similarly, where the waveguide assembly 1178 includesmultiple waveguides. Light 400 is injected into the waveguide 1182 atthe input surface 1382 of the waveguide 1182 and propagates within thewaveguide 1182 by TIR. At points where the light 400 impinges on the DOE1282, a portion of the light exits the waveguide as exit beams 402. Theexit beams 402 are illustrated as substantially parallel but, asdiscussed herein, they may also be redirected to propagate to the eye 4at an angle (e.g., forming divergent exit beams), depending on the depthplane associated with the waveguide 1182. It will be appreciated thatsubstantially parallel exit beams may be indicative of a waveguide withoutcoupling optical elements that outcouple light to form images thatappear to be set on a depth plane at a large distance (e.g., opticalinfinity) from the eye 4. Other waveguides or other sets of outcouplingoptical elements may output an exit beam pattern that is more divergent,which would require the eye 4 to accommodate to a closer distance tobring it into focus on the retina and would be interpreted by the brainas light from a distance closer to the eye 4 than optical infinity.

In some embodiments, a full color image may be formed at each depthplane by overlaying images in each of the component colors, e.g., threeor more component colors. FIG. 8 illustrates an example of a stackedwaveguide assembly in which each depth plane includes images formedusing multiple different component colors. The illustrated embodimentshows depth planes 14 a-14 f, although more or fewer depths are alsocontemplated. Each depth plane may have three component color imagesassociated with it: a first image of a first color, G; a second image ofa second color, R; and a third image of a third color, B. Differentdepth planes are indicated in the figure by different numbers fordiopters (dpt) following the letters G, R, and B. Just as examples, thenumbers following each of these letters indicate diopters (1/m), orinverse distance of the depth plane from a viewer, and each box in thefigures represents an individual component color image. In someembodiments, to account for differences in the eye's focusing of lightof different wavelengths, the exact placement of the depth planes fordifferent component colors may vary. For example, different componentcolor images for a given depth plane may be placed on depth planescorresponding to different distances from the user. Such an arrangementmay increase visual acuity and user comfort and/or may decreasechromatic aberrations.

In some embodiments, light of each component color may be outputted by asingle dedicated waveguide and, consequently, each depth plane may havemultiple waveguides associated with it. In such embodiments, each box inthe figures including the letters G, R, or B may be understood torepresent an individual waveguide, and three waveguides may be providedper depth plane where three component color images are provided perdepth plane. While the waveguides associated with each depth plane areshown adjacent to one another in this drawing for ease of description,it will be appreciated that, in a physical device, the waveguides mayall be arranged in a stack with one waveguide per level. In some otherembodiments, multiple component colors may be outputted by the samewaveguide, such that, e.g., only a single waveguide may be provided perdepth plane.

With continued reference to FIG. 8, in some embodiments, G is the colorgreen, R is the color red, and B is the color blue. In some otherembodiments, other colors associated with other wavelengths of light,including magenta and cyan, may be used in addition to or may replaceone or more of red, green, or blue. In some embodiments, features 198,196, 194, and 192 may be active or passive optical filters configured toblock or selectively light from the ambient environment to the viewer'seyes.

It will be appreciated that references to a given color of lightthroughout this disclosure will be understood to encompass light of oneor more wavelengths within a range of wavelengths of light that areperceived by a viewer as being of that given color. For example, redlight may include light of one or more wavelengths in the range of about620-780 nm, green light may include light of one or more wavelengths inthe range of about 492-577 nm, and blue light may include light of oneor more wavelengths in the range of about 435-493 nm.

In some embodiments, the light source 2040 (FIG. 6) may be configured toemit light of one or more wavelengths outside the visual perceptionrange of the viewer, for example, infrared and/or ultravioletwavelengths. In addition, the incoupling, outcoupling, and other lightredirecting structures of the waveguides of the display 1000 may beconfigured to direct and emit this light out of the display towards theuser's eye 4, e.g., for imaging and/or user stimulation applications.

With reference now to FIG. 9A, in some embodiments, light impinging on awaveguide may need to be redirected to incouple that light into thewaveguide. An incoupling optical element may be used to redirect andincouple the light into its corresponding waveguide. FIG. 9A illustratesa cross-sectional side view of an example of a plurality or set 1200 ofstacked waveguides that each includes an incoupling optical element. Thewaveguides may each be configured to output light of one or moredifferent wavelengths, or one or more different ranges of wavelengths.It will be appreciated that the stack 1200 may correspond to the stack1178 (FIG. 6) and the illustrated waveguides of the stack 1200 maycorrespond to part of the plurality of waveguides 1182, 1184, 1186,1188, 1190, except that light from one or more of the image injectiondevices 1200, 1202, 1204, 1206, 1208 is injected into the waveguidesfrom a position that requires light to be redirected for incoupling.

The illustrated set 1200 of stacked waveguides includes waveguides 1210,1220, and 1230. Each waveguide includes an associated incoupling opticalelement (which may also be referred to as a light input area on thewaveguide), with, e.g., incoupling optical element 1212 disposed on amajor surface (e.g., an upper major surface) of waveguide 1210,incoupling optical element 1224 disposed on a major surface (e.g., anupper major surface) of waveguide 1220, and incoupling optical element1232 disposed on a major surface (e.g., an upper major surface) ofwaveguide 1230. In some embodiments, one or more of the incouplingoptical elements 1212, 1222, 1232 may be disposed on the bottom majorsurface of the respective waveguide 1210, 1220, 1230 (particularly wherethe one or more incoupling optical elements are reflective, deflectingoptical elements). As illustrated, the incoupling optical elements 1212,1222, 1232 may be disposed on the upper major surface of theirrespective waveguide 1210, 1220, 1230 (or the top of the next lowerwaveguide), particularly where those incoupling optical elements aretransmissive, deflecting optical elements. In some embodiments, theincoupling optical elements 1212, 1222, 1232 may be disposed in the bodyof the respective waveguide 1210, 1220, 1230. In some embodiments, asdiscussed herein, the incoupling optical elements 1212, 1222, 1232 arewavelength selective, such that they selectively redirect one or morewavelengths of light, while transmitting other wavelengths of light.While illustrated on one side or corner of their respective waveguide1210, 1220, 1230, it will be appreciated that the incoupling opticalelements 1212, 1222, 1232 may be disposed in other areas of theirrespective waveguide 1210, 1220, 1230 in some embodiments.

As illustrated, the incoupling optical elements 1212, 1222, 1232 may belaterally offset from one another. In some embodiments, each incouplingoptical element may be offset such that it receives light without thatlight passing through another incoupling optical element. For example,each incoupling optical element 1212, 1222, 1232 may be configured toreceive light from a different image injection device 1200, 1202, 1204,1206, and 1208 as shown in FIG. 6, and may be separated (e.g., laterallyspaced apart) from other incoupling optical elements 1212, 1222, 1232such that it substantially does not receive light from the other ones ofthe incoupling optical elements 1212, 1222, 1232.

Each waveguide also includes associated light distributing elements,with, e.g., light distributing elements 1214 disposed on a major surface(e.g., a top major surface) of waveguide 1210, light distributingelements 1224 disposed on a major surface (e.g., a top major surface) ofwaveguide 1220, and light distributing elements 1234 disposed on a majorsurface (e.g., a top major surface) of waveguide 1230. In some otherembodiments, the light distributing elements 1214, 1224, 1234, may bedisposed on a bottom major surface of associated waveguides 1210, 1220,1230, respectively. In some other embodiments, the light distributingelements 1214, 1224, 1234, may be disposed on both top and bottom majorsurface of associated waveguides 1210, 1220, 1230, respectively; or thelight distributing elements 1214, 1224, 1234, may be disposed ondifferent ones of the top and bottom major surfaces in differentassociated waveguides 1210, 1220, 1230, respectively.

The waveguides 1210, 1220, 1230 may be spaced apart and separated by,e.g., gas, liquid, and/or solid layers of material. For example, asillustrated, layer 1218 a may separate waveguides 1210 and 1220; andlayer 1218 b may separate waveguides 1220 and 1230. In some embodiments,the layers 1218 a and 1218 b are formed of low refractive indexmaterials (that is, materials having a lower refractive index than thematerial forming the immediately adjacent one of waveguides 1210, 1220,1230). Preferably, the refractive index of the material forming thelayers 1218 a, 1218 b is 0.05 or more, or 0.10 or more less than therefractive index of the material forming the waveguides 1210, 1220,1230. Advantageously, the lower refractive index layers 1218 a, 1218 bmay function as cladding layers that facilitate total internalreflection (TIR) of light through the waveguides 1210, 1220, 1230 (e.g.,TIR between the top and bottom major surfaces of each waveguide). Insome embodiments, the layers 1218 a, 1218 b are formed of air. While notillustrated, it will be appreciated that the top and bottom of theillustrated set 1200 of waveguides may include immediately neighboringcladding layers.

Preferably, for ease of manufacturing and other considerations, thematerial forming the waveguides 1210, 1220, 1230 are similar or thesame, and the material forming the layers 1218 a, 1218 b are similar orthe same. In some embodiments, the material forming the waveguides 1210,1220, 1230 may be different between one or more waveguides, and/or thematerial forming the layers 1218 a, 1218 b may be different, while stillholding to the various refractive index relationships noted above.

With continued reference to FIG. 9A, light rays 1240, 1242, 1244 areincident on the set 1200 of waveguides. It will be appreciated that thelight rays 1240, 1242, 1244 may be injected into the waveguides 1210,1220, 1230 by one or more image injection devices 1200, 1202, 1204,1206, 1208 (FIG. 6).

In some embodiments, the light rays 1240, 1242, 1244 have differentproperties, e.g., different wavelengths or different ranges ofwavelengths, which may correspond to different colors. The incouplingoptical elements 1212, 122, 1232 each deflect the incident light suchthat the light propagates through a respective one of the waveguides1210, 1220, 1230 by TIR.

For example, incoupling optical element 1212 may be configured todeflect ray 1240, which has a first wavelength or range of wavelengths.Similarly, the transmitted ray 1242 impinges on and is deflected by theincoupling optical element 1222, which is configured to deflect light ofa second wavelength or range of wavelengths. Likewise, the ray 1244 isdeflected by the incoupling optical element 1232, which is configured toselectively deflect light of third wavelength or range of wavelengths.

With continued reference to FIG. 9A, the deflected light rays 1240,1242, 1244 are deflected so that they propagate through a correspondingwaveguide 1210, 1220, 1230; that is, the incoupling optical elements1212, 1222, 1232 of each waveguide deflects light into thatcorresponding waveguide 1210, 1220, 1230 to incouple light into thatcorresponding waveguide. The light rays 1240, 1242, 1244 are deflectedat angles that cause the light to propagate through the respectivewaveguide 1210, 1220, 1230 by TIR. The light rays 1240, 1242, 1244propagate through the respective waveguide 1210, 1220, 1230 by TIR untilimpinging on the waveguide's corresponding light distributing elements1214, 1224, 1234.

With reference now to FIG. 9B, a perspective view of an example of theplurality of stacked waveguides of FIG. 9A is illustrated. As notedabove, the incoupled light rays 1240, 1242, 1244, are deflected by theincoupling optical elements 1212, 1222, 1232, respectively, and thenpropagate by TIR within the waveguides 1210, 1220, 1230, respectively.The light rays 1240, 1242, 1244 then impinge on the light distributingelements 1214, 1224, 1234, respectively. The light distributing elements1214, 1224, 1234 deflect the light rays 1240, 1242, 1244 so that theypropagate towards the outcoupling optical elements 1250, 1252, 1254,respectively.

In some embodiments, the light distributing elements 1214, 1224, 1234are orthogonal pupil expanders (OPE's). In some embodiments, the OPE'sboth deflect or distribute light to the outcoupling optical elements1250, 1252, 1254 and also increase the beam or spot size of this lightas it propagates to the outcoupling optical elements. In someembodiments, e.g., where the beam size is already of a desired size, thelight distributing elements 1214, 1224, 1234 may be omitted and theincoupling optical elements 1212, 1222, 1232 may be configured todeflect light directly to the outcoupling optical elements 1250, 1252,1254. For example, with reference to FIG. 9A, the light distributingelements 1214, 1224, 1234 may be replaced with outcoupling opticalelements 1250, 1252, 1254, respectively. In some embodiments, theoutcoupling optical elements 1250, 1252, 1254 are exit pupils (EP's) orexit pupil expanders (EPE's) that direct light in a viewer's eye 4 (FIG.7).

Accordingly, with reference to FIGS. 9A and 9B, in some embodiments, theset 1200 of waveguides includes waveguides 1210, 1220, 1230; incouplingoptical elements 1212, 1222, 1232; light distributing elements (e.g.,OPE's) 1214, 1224, 1234; and outcoupling optical elements (e.g., EP's)1250, 1252, 1254 for each component color. The waveguides 1210, 1220,1230 may be stacked with an air gap/cladding layer between each one. Theincoupling optical elements 1212, 1222, 1232 redirect or deflectincident light (with different incoupling optical elements receivinglight of different wavelengths) into its waveguide. The light thenpropagates at an angle which will result in TIR within the respectivewaveguide 1210, 1220, 1230. In the example shown, light ray 1240 (e.g.,blue light) is deflected by the first incoupling optical element 1212,and then continues to bounce down the waveguide, interacting with thelight distributing element (e.g., OPE's) 1214 and then the outcouplingoptical element (e.g., EPs) 1250, in a manner described earlier. Thelight rays 1242 and 1244 (e.g., green and red light, respectively) willpass through the waveguide 1210, with light ray 1242 impinging on andbeing deflected by incoupling optical element 1222. The light ray 1242then bounces down the waveguide 1220 via TIR, proceeding on to its lightdistributing element (e.g., OPEs) 1224 and then the outcoupling opticalelement (e.g., EP's) 1252. Finally, light ray 1244 (e.g., red light)passes through the waveguide 1220 to impinge on the light incouplingoptical elements 1232 of the waveguide 1230. The light incouplingoptical elements 1232 deflect the light ray 1244 such that the light raypropagates to light distributing element (e.g., OPEs) 1234 by TIR, andthen to the outcoupling optical element (e.g., EPs) 1254 by TIR. Theoutcoupling optical element 1254 then finally outcouples the light ray1244 to the viewer, who also receives the outcoupled light from theother waveguides 1210, 1220.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B. As illustrated, the waveguides1210, 1220, 1230, along with each waveguide's associated lightdistributing element 1214, 1224, 1234 and associated outcoupling opticalelement 1250, 1252, 1254, may be vertically aligned. However, asdiscussed herein, the incoupling optical elements 1212, 1222, 1232 arenot vertically aligned; rather, the incoupling optical elements arepreferably non-overlapping (e.g., laterally spaced apart as seen in thetop-down view). As discussed further herein, this nonoverlapping spatialarrangement facilitates the injection of light from different resourcesinto different waveguides on a one-to-one basis, thereby allowing aspecific light source to be uniquely coupled to a specific waveguide. Insome embodiments, arrangements including nonoverlappingspatially-separated incoupling optical elements may be referred to as ashifted pupil system, and the in coupling optical elements within thesearrangements may correspond to sub pupils.

Spatially Variable Liquid Crystal Diffraction Gratings

As described above in reference to FIGS. 6 and 7, display systemsaccording to various embodiments described herein may includeoutcoupling optical elements (e.g., optical elements 1282, 1284, 1286,1288, 1290 in FIG. 6), which may include diffraction gratings. Asdescribed above in reference to FIG. 7, light 400 that is injected intothe waveguide 1182 at the input surface 1382 of the waveguide 1182propagates within the waveguide 1182 by total internal reflection (TIR).Referring back to FIG. 7, at points where the light 400 impinges on theoutcoupling optical element 1282, a portion of the light exits thewaveguide as exit beams 402. In some implementations, it may bedesirable to have the optical element 1282 be configured as adiffraction grating having spatially varying optical properties,including diffraction properties. Such configuration may be desirable,for example, when the intensity of the light substantially attenuates asit propagates within the waveguide 1182. Under such circumstances, itmay be desirable have certain diffraction characteristics of the grating1282, e.g., diffraction efficiency (a ratio of diffracted beam intensityto the incident beam intensity) or refractive index, vary along thelight propagation direction, such that uniformity of the intensity ofthe exiting beams 402 are improved. Such configurations may also bedesirable, for example, to intentionally skew the light intensity acrossthe grating 1282 to adapt to spatial and/or angular variation of sensingefficiencies associated with the human eye to maximize the userexperience. Thus, there is a need for outcoupling optical elements,e.g., diffraction gratings, having spatially varying opticalcharacteristics.

For some applications, graded diffraction properties can be achieved bystructurally varying periodic structures of the grating, e.g., by usingsemiconductor processing technology. For example, semiconductor etchingtechnology can be used to holographically pattern gratings into rigidsubstrate materials such as fused silica. By spatially varying the etchprofiles, for instance, correspondingly spatially varying duty cycle orgrating depth can be produced. However, such approaches often involverelatively complex and expensive processes, e.g., multiple etchprocesses. Thus, diffraction gratings with spatially varying opticalproperties, which can be fabricated with relatively simple processingtechnologies, could be beneficial. To this end, according to variousembodiments disclosed herein, liquid crystal materials are used tospatially vary diffraction characteristics across the area of adiffraction gratings, e.g., by spatially varying alignmentcharacteristics or other material properties of the liquid crystalmolecules. In various embodiments, photo-polymerizable liquid crystalmaterials, or reactive mesogens, are used to spatially vary thediffraction characteristics of diffraction gratings. For example, bycoating different areas of a grating with a liquid crystal material andspatially varying its properties, e.g., alignment properties, spatiallyvarying diffraction properties can be generated.

In the following, various embodiments of liquid crystal (LC) gratingshaving varying optical properties, e.g., gradient optical properties,such as varying diffraction properties including diffraction efficiency.Generally, diffraction gratings have a periodic structure, which splitsand diffracts light into several beams travelling in differentdirections. The directions of these beams depend, among other things, onthe period of the periodic structure and the wavelength of the light. Toachieve certain optical properties that spatially vary across the areaof the grating, e.g., spatially varying diffraction efficiencies, forcertain applications such as outcoupling optical element 282 havinguniform intensity of the exiting light beams 402, material properties ofliquid crystals can be spatially varied.

Generally, liquid crystals possess physical properties that may beintermediate between conventional fluids and solids. While liquidcrystals are fluid-like in some aspects, unlike most fluids, thearrangement of molecules within them exhibits some structural order.Different types of liquid crystals include thermotropic, lyotropic, andpolymeric liquid crystals. Thermotropic liquid crystals disclosed hereincan be implemented in various physical states, e.g., phases, including anematic state/phase, a smectic state/phase, a chiral nematic state/phaseor a chiral smectic state/phase.

As described herein, liquid crystals in a nematic state or phase canhave calamitic (rod-shaped) or discotic (disc-shaped) organic moleculesthat have relatively little positional order, while having a long-rangedirectional order with their long axes being roughly parallel. Thus, theorganic molecules may be free to flow with their center of masspositions being randomly distributed as in a liquid, while stillmaintaining their long-range directional order. In some implementations,liquid crystals in a nematic phase can be uniaxial; i.e., the liquidcrystals have one axis that is longer and preferred, with the other twobeing roughly equivalent. In other implementations, liquid crystals canbe biaxial; i.e., in addition to orienting their long axis, the liquidcrystals may also orient along a secondary axis.

As described herein, liquid crystals in a smectic state or phase canhave the organic molecules that form relatively well-defined layers thatcan slide over one another. In some implementations, liquid crystals ina smectic phase can be positionally ordered along one direction. In someimplementations, the long axes of the molecules can be oriented along adirection substantially normal to the plane of the liquid crystal layer,while in other implementations, the long axes of the molecules may betilted with respect to the direction normal to the plane of the layer.

As described herein, nematic liquid crystals are composed of rod-likemolecules with the long axes of neighboring molecules approximatelyaligned to one another. To describe this anisotropic structure, adimensionless unit vector n called the director, may be used to describethe direction of preferred orientation of the liquid crystal molecules.

As describe herein, liquid crystals in a nematic state or a smecticstate can also exhibit chirality. In a chiral phase, the liquid crystalscan exhibit a twisting of the molecules perpendicular to the director,with the molecular axis parallel to the director. The finite twist anglebetween adjacent molecules is due to their asymmetric packing, whichresults in longer-range chiral order.

As described herein, liquid crystals in a chiral smectic state or phasecan be configured such that the molecules have positional ordering in alayered structure, with the molecules tilted by a finite angle withrespect to the layer normal. In addition, chirality can inducesuccessive azimuthal twists from one layer to the next, producing aspiral twisting of the molecular axis along the layer normal.

As described herein, liquid crystals displaying chirality can bedescribed as having a chiral pitch, p, which can refer to the distanceover which the liquid crystal molecules undergo a full 360° twist. Thepitch, p, can change when the temperature is altered or when othermolecules are added to the liquid crystal host (an achiral liquid hostmaterial can form a chiral phase if doped with a chiral material),allowing the pitch of a given material to be tuned accordingly. In someliquid crystal systems, the pitch is of the same order as the wavelengthof visible light. As described herein, liquid crystals displayingchirality can also be described as having a twist angle, which canrefer, for example, to the relative azimuthal angular rotation betweenan uppermost liquid crystal molecule and a lowermost liquid crystalmolecule across a thickness of the liquid crystal material.

According to various embodiments described herein, liquid crystalshaving various states or phases as described above can be configured tooffer various desirable material properties for diffraction gratings,including, e.g., birefringence, optical anisotropy, andmanufacturability using thin-film processes. For example, by changingsurface conditions of liquid crystal layers and/or mixing differentliquid crystal materials, grating structures that exhibit spatiallyvarying diffraction properties, e.g., gradient diffraction efficiencies,can be fabricated.

As described herein, “polymerizable liquid crystals” may refer to liquidcrystal materials that can be polymerized, e.g., in-situphotopolymerized, and may also be described herein as reactive mesogens(RM).

It will be appreciated that the liquid crystal molecules may bepolymerizable in some embodiments and, once polymerized, may form alarge network with other liquid crystal molecules. For example, theliquid crystal molecules may be linked by chemical bonds or linkingchemical species to other liquid crystal molecules. Once joinedtogether, the liquid crystal molecules may form liquid crystal domainshaving substantially the same orientations and locations as before beinglinked together. For ease of description, the term “liquid crystalmolecule” is used herein to refer to both the liquid crystal moleculesbefore polymerization and to the liquid crystal domains formed by thesemolecules after polymerization.

According to particular embodiments described herein,photo-polymerizable liquid crystal materials can be configured to form adiffraction grating, whose material properties, including birefringence,chirality, and ease for multiple-coating, can be utilized to creategratings with graded diffraction efficiencies, as changes in thesematerial properties (e.g., birefringence, chirality, and thickness)result in variations in diffraction efficiencies accordingly.

It will be appreciated that, as described herein, a “transmissive” or“transparent” structure, e.g., a transparent substrate, may allow atleast some, e.g., at least 20, 30 or 50%, of an incident light, to passtherethrough. Accordingly, a transparent substrate may be a glass,sapphire or a polymeric substrate in some embodiments. In contrast, a“reflective” structure, e.g., a reflective substrate, may reflect atleast some, e.g., at least 20, 30, 50, 70, 90% or more of the incidentlight, to reflect therefrom.

Optical properties of a grating are determined by the physicalstructures of the grating (e.g., the periodicity, the depth, and theduty cycle), as well as material properties of the grating (e.g.,refractive index, absorption, and birefringence). When liquid crystalsare used, optical properties of the grating can be controlled bycontrolling, e.g., molecular orientation or distribution of the liquidcrystal materials. For example, by varying molecular orientation ordistribution of the liquid crystal material across the grating area, thegrating may exhibit graded diffraction efficiencies. Such approaches aredescribed in the following, in reference to the figures.

In various embodiments, a diffraction grating comprises a substrate anda plurality of different diffracting zones having a periodicallyrepeating lateral dimension corresponding to a grating period adaptedfor light diffraction. The diffraction grating further comprises aplurality of different liquid crystal layers corresponding the differentdiffracting zones, wherein the different liquid crystal layers haveliquid crystal molecules that are aligned differently, such that thedifferent diffracting zones have different optical properties associatedwith light diffraction.

Photo-Aligned Spatially Variable Liquid Crystal Diffraction Gratings

Referring to FIGS. 10A-10C, cross-sectional side views (viewed along thex-z plane) of diffraction gratings 100A-100C according to someembodiments are illustrated. Each of the diffraction gratings 100A-100Ccomprises a substrate 104 and a plurality of diffracting zones, i.e.,diffracting zones 108A-1, 108A-2, . . . and 108A-n as illustrated inFIG. 10A, diffracting zones 108B-1, 108B-2, . . . and 108B-n asillustrated in FIG. 10B, and diffracting zones 108C-1, 108C-2, . . . and108C-n as illustrated in FIG. 10C.

The diffracting zones of each of the diffraction gratings 100A-100C havea periodically repeating lateral dimension or a grating period A andinclude corresponding liquid crystal layers formed of liquid crystalmolecules 112. In the illustrated embodiment and throughout thisdisclosure, the liquid crystal molecules 112 can be in a nematic stateor a smectic state, or a mixture thereof, among other possible states ofliquid crystal molecules. In the illustrated embodiment and throughout,various embodiments can have the grating period A that is between about100 nm and about 10,000 nm, between about 200 nm and about 2000 nm orbetween about 300 nm and about 1000 nm, such that the plurality ofdiffracting zones are configured to diffract visible light.

The diffracting zones 108A-1, 108A-2, . . . 108A-n of the diffractiongrating 100A have corresponding liquid crystal layers 116A-1, 116A-2, .. . 116A-n, respectively; diffracting zones 108B-1, 108B-2, . . . 108B-nof the diffraction grating 100B have corresponding liquid crystal layers116B-1, 116B-2, . . . 116B-n, respectively; and diffracting zones108C-1, 108C-2, . . . 108C-n of the diffraction grating 100C havecorresponding liquid crystal layers 116C-1, 116C-2 and 116C-n,respectively.

It will be understood herein and throughout the specification that “n”can be a suitable integer for representing the number of differentzones. For example, diffracting zones 108B-1, 108B-2, . . . 108B-nindicates that there can be n number of diffracting zones, where n is aninteger. The number (n) of diffracting zones that is omitted from theFigures can be, for example, between 1 and about 500, between about 1and about 200 or between about 1 and about 100. In some implementations,optical properties of a diffraction grating can vary continuously acrossthe surface. In one implementation, for example, there can be onegrating period A per diffracting zone for at least some of thediffracting zones. When each diffracting zone has one grating period A,the number (n) of diffracting zones can represent the number of gratingperiods A.

It will be understood herein and throughout the specification that, “ .. . ,” when indicated in a Figure, can represent the presence ofadditional diffracting zones between the illustrated zones, which can becontiguously connected and similar or the same as any other adjacentlyillustrated zone. In addition, “ . . . ” can also represent anarrangement of diffracting zones that periodically repeat any suitablenumber of times.

Each of the liquid crystal layers 116A-1, 116A-2 and 116A-n of thediffraction grating 100A in turn has differently arranged first andsecond diffracting regions 116A-1L and 116A-1R, 116A-2L and 116A-2R, . .. and 116A-nL and 116A-nR, respectively. Similarly, each of the liquidcrystal layers 116B-1, 116B-2 and 116B-n of the diffraction grating 100Bin turn has differently arranged first and second diffracting regions116B-1L and 116B-1R, 116B-2L and 116B-2R, . . . and 116B-nL and 116B-nR,respectively. Similarly, each of the liquid crystal layers 116C-1,116C-2 and 116C-n of the diffraction grating 100C in turn hasdifferently arranged first and second diffracting regions 116C-1L and116C-1R, 116C-2L and 116C-2R, . . . and 116C-nL and 116C-nR,respectively. The regions are sometimes referred to as domains of liquidcrystal molecules

Still referring to FIGS. 10A-10C, each of the different diffractingzones further comprises an alignment layer 120 interposed between thesubstrate 104 and the corresponding liquid crystal layer, wherein thealignment layer is configured to induce the alignment of the liquidcrystal molecules in different regions of each zone. Interposed betweenthe substrate 104 and the first/second diffracting regions116A-1L/116A-1R, 116A-2L/116A-2R, . . . and 116A-nL/116A-nR of thediffraction grating 100A of FIG. 10A are first and second alignmentlayers 120A-1L/120A-1R, 120A-2L/120A-2R, . . . and 120A-nL/120A-nR,respectively. Similarly interposed between the substrate 104 and thefirst/second diffracting regions 116B-1L/116B-1R, 116B-2R/116B-2R, . . .and 116B-nL/116B-nR of the diffraction grating 100C of FIG. 10B arefirst/second alignment layers 120B-1L/120B-1R, 120B-2L/120B-2R, . . .and 120B-nL/120B-nR, respectively. Similarly, interposed between thesubstrate 104 and differently arranged first/second diffracting regions116C-1L/116C-1R, 116C-2L/116C-2R, . . . and 116C-nL/116C-nR of thediffraction grating 100C of FIG. 10C are first/second alignment layers120C-1L/120C-1R, 120C-2L/120C-2R, . . . and 120C-nL/120C-nR,respectively.

Herein and throughout the disclosure, an alignment direction ofelongated liquid crystal molecules can refer to the direction ofelongation of the liquid crystal molecules, or the direction of thedirector vector n.

Herein and throughout the disclosure, a tilt angle or a pre-tilt angle Φcan refer to an angle measured in a plane perpendicular to a majorsurface (in an x-y plane) of the liquid crystal layers or of thesubstrate, e.g., the x-z plane, and measured between an alignmentdirection and the major surface or a direction parallel to the majorsurface, e.g., the x-direction.

Herein and throughout the disclosure, an azimuthal angle or a rotationangle φ is used to describe an angle of rotation about an axis normal toa major surface (in an x-y plane), which is measured in a plane parallelto a major surface of the liquid crystal layers or of the substrate,e.g., the x-y plane, and measured between an alignment direction and adirection parallel to the major surface, e.g., the y-direction.

Herein and throughout the disclosure, when an alignment angle such as apre-tilt angle Φ or a rotation angle φ are referred to as beingsubstantially the same between different regions, it will be understoodthat an average alignment angles can, for example, be within about 1%,about 5% or about 10% of each other although the average alignment canbe larger in some cases.

Herein and throughout the specification, a duty cycle can, for example,refers to a ratio between a first lateral dimension of a first regionhaving liquid crystal molecules aligned in a first alignment direction,and the grating period of the zone having the first region. Whereapplicable, the first region corresponds to the region in which thealignment of the liquid crystals does not vary between different zones.

Still referring to FIGS. 10A-10C, each zone of the diffraction gratings100A, 100B and 100C include first and second regions that alternate inthe x-direction. Each of the first regions 116A-1L, 116A-2L, . . . and116A-nL of the diffraction grating 100A, each of the first regions116B-1L, 116B-2L, . . . and 116B-nL of the diffraction grating 100B andeach of the first regions 116C-1L, 116C-2L, . . . and 116A-nL of thediffraction grating 100C have liquid crystal molecules 112 that arealigned substantially along the same first alignment direction and havea first pre-tilt angle Φ that is substantially the same. Each of thesecond regions 116A-1R, 116A-2R, . . . and 116A-nR of the diffractiongrating 100A, each of the second regions 116B-1R, 116B-2R, . . . and116B-nL of the diffraction grating 100B and each of the second regions116C-1R, 116C-2R, . . . and 116C-nR of the diffraction grating 100C haveliquid crystal molecules 112 that are aligned substantially along asecond alignment direction different from the first alignment directionand have second pre-tilt angles Φ that are different, e.g., greater,than the first pre-tilt angle Φ of the respective first regions.

In each of the diffraction gratings 100A-100C of FIGS. 10A-10C,respectively, at least some of the diffracting zones have liquid crystallayers formed of liquid crystal molecules that are spatially arrangeddifferently, e.g., have different pre-tilt angles from each other (FIGS.10A and 10C), or have laterally varying duty cycles (FIGS. 10B and 10C),such that the diffracting zones have different optical properties, e.g.,different refractive indices and different diffraction efficiencies,according to embodiments.

In particular, referring to diffraction grating 100A of FIG. 10A, inaddition to having alignment directions and pre-tilt angles Φ that aredifferent from the first pre-tilt angle Φ of the first regions 116A-1L,116A-2L, . . . and 116A-nL, the liquid crystal molecules of differentsecond regions 116A-1R, 116A-2R, . . . and 116A-nR are aligned alongsecond alignment directions that are different from each other. Forexample, in the illustrated embodiment, the zones 108A-1, 108A-2 and108A-n are arranged such that the first regions and second regionsalternate in the x-direction, where each of the first regions 116A-1L,116A-2L, . . . and 116A-nL has substantially the same pre-tilt angle Φ,while the second regions 116A-1R, 116A-2R, . . . and 116A-nR havepre-tilt angles Φ that are different from each other. By way of example,the first regions 116A-1L, 116A-2L, . . . and 116A-nL have a pre-tiltangle Φ that is between about ±15 degrees or between about ±10 degreesor between about ±5, e.g., 0 degrees. The second regions 116A-1R,116A-2R, . . . and 116A-nR can have pre-tilt angles Φ that are differentfrom each other and are each between about 60 degrees and about 90degrees or between about 65 degrees and about 85 degrees, for instanceabout 75 degree; between about 35 degrees and about 65 degrees orbetween about 40 degrees and about 60 degrees, for instance about 50degrees; between about 10 degrees and about 40 degrees or between about15 degrees and about 35 degrees, for instance about 25 degrees.

Still referring to FIG. 10A, in some embodiments, as illustrated, thesecond regions 116A-1R, 116A-2R, . . . and 116A-nR can have tilt anglesΦ that vary, e.g., increase or decrease in one direction in a lateraldirection, such that a gradient in diffraction properties is created. Inother embodiments, the second regions 116A-1R, 116A-2R, . . . and116A-nR can have tilt angles Φ that do not vary in one direction in thelateral direction.

Still referring to FIG. 10A, the duty cycle, defined above, can bebetween about 10% and about 30%, between about 30% and about 50%,between about 40% and 60% (e.g., about 50%), between about 50% and about70% or between about 70% and about 90%.

Referring now to FIG. 10B, the diffraction grating 100B share somecommon features as the diffraction grating 100A of FIG. 10A. However,unlike the diffracting grating 100B of FIG. 10A, while the liquidcrystal molecules of different second regions 116B-1R, 116B-2R, . . .and 116B-nR have pre-tilt angles Φ that are different from the firstpre-tilt angle Φ of the first regions 116B-1L, 116B-2L, . . . and116B-nL, they are not aligned differently from each other. For example,in the illustrated embodiment, the zones 108B-1, 108B-2 and 108B-n arearranged such that the first regions and second regions alternate in thex-direction, where each of the first regions 116B-1L, 116B-2L, . . . and116B-nL has substantially the same first pre-tilt angle Φ, and each ofthe second regions 116B-1R, 116B-2R, . . . and 116B-nR has substantiallythe same second pre-tilt angles Φ. The first and second pre-tilt anglesof the first and second regions can have any of the values discussedabove with respect to the diffraction grating 100A of FIG. 10A.

Still referring to FIG. 10B, unlike the grating 100A of FIG. 10A, thezones 116B-1, 116B-2 and 116B-3 have substantially the same pre-tiltangle, e.g., between about 0 to 90 degrees, while having a duty cyclebetween about 40% and about 60%, for instance about 50%; between about30% and about 50%, for instance about 40% and a duty cycle between about20% and about 40%, for instance about 30%, respectively, such that thediffraction grating 100B has spatially varying optical properties.

Still referring to FIG. 10B, in some embodiments, as illustrated, thezones can have duty cycles that vary, e.g., increase or decrease in onedirection in a lateral direction, such that a gradient in opticalproperties is created. In other embodiments, the duty cycles do not varyin one direction in the lateral direction.

Referring now to FIG. 10C, the illustrated diffraction grating 100Ccombines features similar to those described above with respect to thediffraction gratings 100A and 100B of FIGS. 10A and 10B. In particular,the liquid crystal molecules of different second regions 116C-1R,116C-2R, . . . and 116C-nR can have pre-tilt angles Φ that are differentfrom the first pre-tilt angle Φ of the first regions 116C-1L, 116C-2L, .. . and 116C-nL, and aligned differently from each other. In addition,the duty cycle varies between adjacent zones across a lateral direction,e.g., x-direction. The first and second pre-tilt angles of the first andsecond regions can have any of the values discussed above with respectto the diffraction grating 100A of FIG. 10A. In addition, the duty cyclevariation between adjacent zones across a lateral direction, e.g.,x-direction, can also have values discussed above with respect to thediffraction grating 100B of FIG. 10B.

In the diffraction gratings 100A-100C illustrated in FIGS. 10A-10C andthroughout the disclosure, it will be appreciated that, in addition tothe grating period and duty cycle discussed above, the diffractionproperties can be further defined by, among other things, the thicknessand the refractive index of the liquid crystal layer 116. According tovarious embodiments disclosed herein, the thickness of the liquidcrystal layers disclosed herein can have a thickness between about 1 μmand about 100 μm, between about 0.5 μm and about 20 μm or between about0.1 μm and about 10 μm. An average refractive index of the liquidcrystal layers disclosed herein can be between about 1.8 and about 2.0,between about 1.6 and about 1.8 or between about between about 1.4 andabout 1.2. The resulting average diffraction efficiency of variousdiffraction gratings disclosed herein can be between about 1% and about80%, between about 1% and about 50% or between about between about 5%and about 30%.

As a result of implementing various embodiments disclosed herein andthroughout the disclosure, different zones can have indices ofrefraction that vary between about −30% and about +30%, between about−20% and about +20% or between about −10% and about +10% across thesurface area of the diffraction grating, with respect to the averagerefractive index. As a further result, different zones can havediffraction efficiencies that vary between about 1% and about 80%,between about 1% and about 50% or between about 1% and about 30% acrossthe surface area of the diffraction grating, with respect to the averagediffraction efficiency.

FIGS. 11A and 11B illustrate a method for fabricating diffractiongratings having liquid crystal molecules with non-uniform pre-tiltangles across the surface such as, e.g., diffraction gratings 100A-100Cof FIGS. 10A-10C described above, using photo-alignment techniques,according to embodiments.

Referring to an intermediate structure 100 a of FIG. 11A, a substrate104 is provided, on which a photo-alignment layer 120 is formed. Thesubstrate 104 can be an optically transparent substrate that istransparent in the visible spectrum, such as, e.g., silica-based glass,quartz, sapphire, indium tin oxide (ITO) or polymeric substrates, toname a few examples.

As described herein, a photo-alignment layer can refer to a layer onwhich, when a liquid crystal molecules are deposited, the liquid crystalmolecules become oriented, for example, due to anchoring energy exertedon the liquid crystal molecule by the photo-alignment layer. Examples ofphoto-alignment layers include polyimide, linear-polarizationphotopolymerizable polymer (LPP), azo-containing polymers,courmarine-containing polymers and cinnamate-containing polymers, toname a few.

The photo-alignment layer 120 can be formed by dissolving precursors,e.g., monomers, in a suitable solvent and coating, spin-coating, thesurface of the substrate 104 with the solution. The solvent canthereafter be removed from the coated solution.

After coating and drying the photo-alignment layer 120, a photomask 130can be used to expose different regions of the underlyingphoto-alignment layer 120 to different doses of light and/or differentpolarizations of light. For example, the regions of the photo-alignmentlayer 120 that are to be exposed differently can correspond to first(e.g., left) and second (e.g., right) regions of each of zones 108A-1and 108A-2 described above with respect to the diffraction grating 100Aof FIG. 10A.

In some embodiments, the photo-alignment layer 120 can be configuredsuch that the resulting liquid crystal molecules are orientedsubstantially parallel to the polarization direction of the exposurelight (e.g., the azimuthal angle φ and the linear polarization angle ofthe exposure light are substantially the same). In other embodiments,the photo-alignment layer 120 can be configured such that the liquidcrystal molecules are oriented substantially orthogonal to thepolarization direction of the exposure light (e.g., the azimuthal angleφ and the linear polarization angle of the exposure light aresubstantially offset by about +/−90 degrees).

In one example, the photomask 130 can be a gray-scale mask having aplurality of mask regions 130 a-130 d that are at least partiallytransparent and possibly have one or more opaque regions. Different onesof the plurality of mask regions 130 a-130 d may be configured totransmit different amounts of the incident light 140, such thattransmitted light 140 a-140 d transmitted through different ones of theplurality of mask regions 130 a-130 d has varying intensities that areproportional to the relative transparency of the different mask regions130 a-130 d to the incident light 140. However, embodiments are not solimited and other mask types can be used. For example, the photomask 130can be a binary mask having the plurality of mask regions 130 a-130 deach being fully or nearly fully transparent or fully or nearly fullyopaque, such that transmitted light 140 a-140 d transmitted through theplurality of mask regions 130 a-130 d has binary intensities.

The photomask 130 can be formed of a suitable material which at leastpartially absorbs UV light. In some embodiments, the varying intensitiesof transmitted light across different mask regions 130 a-130 d can beachieved by using different materials (e.g., having different absorptioncoefficients) in the different regions, materials doped possiblydifferent amounts in different regions or by using different thicknessesin the different regions. Other types of masks can be used. In someembodiments, the photomask 130 can contact the underlyingphoto-alignment layer 120, while in other embodiments, the photomask 130does not contact the underlying photo-alignment layer 120.

The incident light can be UV light, e.g., from a high pressure Hg-lamp,e.g., for their spectral lines at 436 nm (“g-line”), 405 nm (“h-line”)and 365 nm (“i-line”). However, embodiments are not so limited, and theincident light can be any suitable light to which the photo-alignmentlayer 120 is responsive, including visible light. When polarized, theincident UV-light can be polarized using a suitable polarizer.Accordingly, in various cases, the mask is transmissive to UV-light.Other ways of patterning besides utilizing a photo-mask can be employed.

In some embodiments, the incident light 140 can be generated for aduration by using a single uniform incident light source. However,embodiments are not so limited, and in other embodiments, the incidentlight 140 can vary in intensity across different mask regions 130 a-130d. Furthermore, in yet other embodiments, the incident light 140 can beselectively generated for different durations across different maskregions 130 a-130 d.

Furthermore, in the illustrated embodiment, the incident light 140 canbe polarized, e.g., linearly polarized, as schematically depicted bypolarization vectors 134 a-134 d. However, the incident light 140according to other embodiments can be circularly or ellipticallypolarized. In some embodiments, the polarization vectors 134 a-134 d canrepresent different polarization angles, while in some otherembodiments, the incident light 140 can have a single polarizationangle.

Without being bound to any theory, the combination of thephoto-alignment material and the different doses and polarization(s) ofthe transmitted light 140 a-140 d causes various regions of theresulting photo-alignment layer 120 to exert different amounts ofanchoring energy on the overlying liquid crystal molecules, therebycausing the different orientations of the liquid crystal molecules, asdescribed herein. Other methods that may or may not employ masks may beused as well.

Referring to FIG. 11B, after exposing the photo alignment layer 120 tovarying doses of transmitted light 140 a-140 d using various techniquesdescribed above, a liquid crystal layer 116 can be formed on the photoalignment layer 120.

The liquid crystal layer 116 can be formed by dissolving liquid crystalprecursors, e.g., monomers, in a suitable solvent and coating, e.g.,spin-coating, the surface of the alignment layer 120 with the solutionhaving the liquid crystal precursors dissolved therein. The solvent canthereafter be removed from the coated solution

In various embodiments, the reactive mesogen materials used for formingthe liquid crystal layer 116 include liquid crystalline mono- ordi-acrylate, for example.

Because of the different doses and or polarization angle of lightreceived by different regions of the photo alignment layer 120 asdescribed above, the liquid crystal layer, e.g., as-deposited, forms theliquid crystal layers 116A-1 and 116A-2 in zones 108A-1 and 108A-2,respectively. The liquid crystal layers 116A-1 and 116A-2, in turn, havefirst and second diffracting regions 116A-1L and 116A-1R, and 116A-2Land 116A-2R, respectively. As described above with respect to FIG. 10A,the first regions and second regions alternate in the x-direction, whereeach of the first regions 116A-1L and 116A-2L has substantially the samefirst pre-tilt angle Φ, while the second regions 116A-1R and 116A-2Rhave pre-tilt angles Φ that are different from each other and from thefirst pre-tilt angle of the first regions. Without being bound to anytheory, in some types of photo-alignment materials, exposure of theunderlying photo-alignment layer 120 to light is believed to increasethe anchoring energy that causes the in-plane alignment of the liquidcrystal molecules. As a result, in these photo-alignment materials,increasing the exposure leads to a corresponding reduction in thepre-tile angle Φ of the liquid crystal layers formed thereon, accordingto embodiments. However, in other types of photo-alignment materials,exposure of the underlying photo-alignment layer 120 to light isbelieved to decrease the anchoring energy that causes the in-planealignment of the liquid crystal molecules. As a result, in thesephoto-alignment materials, increasing the exposure leads to acorresponding increase in the pre-tilt angle Φ of the liquid crystallayers formed thereon, according to embodiments.

Thus, according to embodiments, the degree of tilt, as measured by thepre-tilt angle Φ, is inversely proportional to the dose of transmittedlight received by the underlying photo-alignment layer 120. For example,in the illustrated embodiment, the photo-alignment layers 120A-1L and120A-2L receive the highest amount of incident light, followed by thealignment layer 120A-1R, followed by the alignment layer 120-2R. As aresult, the resulting pre-tilt angles are highest for the second region116A-2R of the zone 108A-2, followed by the second region 116A-1R of thezone 108A-1, followed by the first regions 116A-1L and 116A-2L of thezones 108A-1 and 108A-2, respectively.

FIGS. 12A-12C illustrate another method for fabricating diffractiongratings having non-uniform pre-tilt angles, e.g., diffraction gratings100A-100C of FIGS. 10A-10C described above, using photo-alignmenttechniques, according to embodiments. In particular, in the illustratedembodiment, the method uses multiple exposures of the alignment layersprior to formation of the liquid crystals.

In the illustrated method of FIGS. 12A-12C, similar to the methodillustrated with respect to FIGS. 11A-11B, a substrate 104 is providedon which a photo-alignment layer 120 is formed. However, unlike themethod illustrated with respect to FIGS. 11A-11B, prior to using aphotomask 130 to expose different regions of the underlyingphoto-alignment layer 120 to different doses of light and/or differentpolarizations of light, the photo-alignment layer 120 is exposed to aprimary (e.g., blanket) pattern of light using a first incident light140A. The primary pattern of light may be produced using, e.g., blanketexposing using, e.g., a blanket semitransparent gray scale mask (notshown). In the illustrated embodiment, a mask may be omitted for theblanket exposure to the primary pattern of light.

The first incident light 140A can be polarized, e.g., linearly polarizedat a first polarization angle, as schematically depicted by polarizationvectors 134 a-134 d. The first incident light 140A that is linearlypolarized can create a uniform alignment of the liquid crystalmolecules. Subsequent to exposing to the primary (e.g., blanket) patternof light, the alignment layer 120 may be further exposed to a secondarypattern of light using a second incident light 140B and a photomask 130,which is configured to expose different regions of the underlyingphoto-alignment layer 120 to different doses of light and/or differentpolarizations of light, in a manner substantially similar to the methoddescribed above with respect to FIGS. 11A-11B. For example, differentregions of the photo-alignment layer 120 corresponding to first (e.g.,left) and second (e.g., right) regions of each of zones 108A-1 and108A-2 as described above with respect to the diffraction grating 100Acan be exposed to different doses and/or different polarization oflight. Unlike the first incident light 140A, the second incident light140B can be unpolarized or circularly polarized. The second incidentlight 140B that is unpolarized or circularly polarized can redistributealignment directions of the liquid crystal molecules. The resultingdiffraction grating 100A is similar to that described above with respectto FIG. 11B, where first regions and second regions alternate in thex-direction, and where each of the first regions 116A-1L and 116A-2L hassubstantially the same first pre-tilt angle Φ, while the second regions116A-1R and 116A-2R have pre-tilt angles Φ that are different from eachother and from the first pre-tilt angle of the first regions.

The second incident light 140B can be polarized, e.g., linearlypolarized at a second polarization angle different from, e.g.,orthogonal to, the second polarization angle of the first incident light140A, as schematically depicted by polarization vectors 134 e-134 h. Insome other embodiments, the first and second polarization angles are thesame. In yet some other embodiments, the first and second polarizationangles are different while not orthogonal. Furthermore, the secondincident light 140B according to other embodiments can be circularly orelliptically polarized, having similar or different polarizationorientation relative to the first incident light 140A.

In the embodiments described above in reference to FIGS. 11A-11B andFIGS. 12A-12C, methods of controlling pre-tilt angles of liquid crystalsusing photo-alignment technique have been described. However, it will beappreciated that other embodiments are possible, including a processreferred to as micro-rubbing, in which the alignment layers are rubbedwith a metallic object, e.g., a metallic sphere under a load. Forexample, a metallic sphere is in direct contact with the alignment layermay be moved across the alignment layer to creating micrometer-sizedrubbed lines, which induce the pre-tilting of the subsequently depositedliquid crystals. In yet other embodiments, alignment materialspre-configured to induce different pre-tilt angles can be deposited,instead of post-treating them to induce the pre-tilting of the liquidcrystal molecules.

Referring now to FIGS. 13A and 13B, cross-sectional (x-z plane) views ofdiffraction gratings 103A and 103B according to some other embodimentsare illustrated. The diffraction gratings 103A and 103B can bepolarization gratings (PGs), which are configured to locally modify thepolarization state of transmitted light, which can be achieved byspatially varying birefringence and/or dichroism. While not shown forclarity, each of the diffraction gratings 103A and 103B comprises asubstrate and an alignment layer formed thereon, and a plurality ofdifferently arranged diffracting zones 154A-1 and 154A-2 in FIG. 13A anddiffracting zones 154B-1 and 154B-2 in FIG. 13B. The diffracting zones154A-1 and 154A-2 of the diffraction grating 103A have correspondingliquid crystal layers 144A-1 and 144A-2, respectively and diffractingzones 154A-1 and 154A-2 of the diffraction grating 103B havecorresponding liquid crystal layers 154B-1 and 154B-2, respectively.

Each of the liquid crystal layers 144A-1 and 144A-2 of the diffractiongrating 103A in turn has a plurality of differently arranged diffractingregions 144A-1 a through 144A-1 g and 144A-2 a through 144A-2 g,respectively. Similarly, each of the liquid crystal layers 144B-1 and144B-2 of the diffraction grating 103B in turn has a plurality ofdifferently arranged diffracting regions 144B-1 a through 144B-1 g and144B-2 a through 144A-2 g, respectively.

Referring to the diffraction grating 103A of FIG. 13A, each of theplurality of regions 144A-1 a to 144A-1 g of the zone 154A-1 and each ofthe plurality of regions 144A-2 a to 144A-2 g of the zone 154A-2 hasliquid crystal molecules 112 that are aligned substantially along thesame alignment direction within the same region. The liquid crystalmolecules 112 of all regions of the zone 154A-1 have a first pre-tiltangle Φ that is substantially the same. In contrast, the liquid crystalmolecules 112 of different regions of the zone 154A-2 have differentpre-tilt angles Φ. While in the illustrated embodiment, the pre-tiltangle Φ of a central region (144A-2 d) of the zone 154A-2 has a pre-tiltangle Φ that is the smallest with increasing pre-tilt angles Φ forincreasingly outer regions of the zone 154A-2, embodiments are not solimited. In addition, while the central region (144A-2 d) in theillustrated embodiment has a pre-tilt angle Φ that is similar to thefirst pre-tilt angle Φ of the zone 154A-1, embodiments are not solimited. The pre-tilt angles of different regions of the diffractiongrating 103A can have any of the magnitudes described supra with respectto FIGS. 10A-10C.

Still referring to FIG. 13A, in the illustrated embodiment, the liquidcrystal molecules 112 of different regions of the zone 154A-1 havedifferent azimuthal angles cp. However, embodiments are not so limitedand in other embodiments, the liquid crystal molecules 112 of differentregions of the zone 154A-1 can have the same azimuthal angles φ. Theazimuthal angles of different regions of the diffraction grating 103Acan have any of the magnitudes described infra with respect to FIGS.15A-15C.

Referring to the diffraction grating 103B of FIG. 13B, similar to thediffraction grating 103A of FIG. 13A, each of the plurality of regions144B-1 a to 144B-1 g of the zone 154B-1 has liquid crystal molecules 112that are aligned substantially along the same alignment direction withinthe same region. Similar to the zone 154A-2 of the diffraction grating103A of FIG. 13A, the liquid crystal molecules 112 of different regionsof the zone 154B-1 have substantially different pre-tilt angles Φ andsubstantially different azimuthal angles φ. In contrast, each of theplurality of regions 144B-2 a to 144B-2 g of the zone 154B-2 has liquidcrystal molecules 112 that are aligned substantially differently withinthe same region. That is, the individual liquid crystal molecules 112 ofeach region of the zone 154B-2 have substantially different pre-tiltangles Φ and substantially different azimuthal angles φ. For example,the liquid crystal molecules 112 of each region of the zone 154B-2 canhave chirality, as described more in detail with respect to FIGS. 19Aand 19B, infra.

Still referring to FIGS. 13A and 13B, while specific combinations ofzones and regions within different zones have been presented asexamples, it will be appreciated that the zone and regions within thezones can be mixed and matched. For example, a combination of the zone154A-1 of FIG. 13A and the zone 154B-2 of FIG. 13B in a diffractiongrating is possible.

FIGS. 14A-14B illustrate another method for fabricating diffractiongratings having non-uniform pre-tilt angles, e.g., diffraction gratings103A and 103B of FIGS. 13A and 13B, respectively, using photo-alignmenttechniques, according to embodiments. In particular, in the illustratedembodiment, the method comprises polarization interference holographicexposure using a gray-scale mask, according to embodiments.

Polarization interference holographic exposure is a technique to createan interference pattern using multiple beams of coherent light. Whilemost conventional holography uses an intensity modulation, polarizationholography involves a modulation of the polarization state to create aninterference pattern.

Referring to FIG. 14A, in the illustrated method, processes leading upto exposing the photo-alignment layer 120 to UV light is similar to themethod described above with respect to FIGS. 11A-11B. In particular, thephoto-alignment layer 120 is formed on a substrate 104 and a gray scalemask 130 is disposed partially over the photo-alignment layer 120.Thereafter, a plurality of coherent light beams 142 a, 142 b havingdifferent polarizations are directed to the plurality of differentlyarranged diffracting zones 154A-1 and 154A-2. In the illustratedembodiment, the light beams 142 a and 142 b include orthogonal circularpolarized light beams. However, the light beams 142 a and 142 b caninclude non-orthogonal circular polarized light beams, for example. Inthe illustrated embodiment, the zone 154A-1 is exposed while the zone154A-2 is masked with the gray scale mask 130. The plurality of lightbeams 142 a and 142 b are positioned and polarized such that theresulting interference effect results in the liquid crystal layers144A-1 and 144A-2 of the diffraction grating 103A having a plurality ofdifferently arranged diffracting regions 144A-1 a through 144A-1 g and144A-2 a through 144A-2 g, respectively, as described above with respectto FIG. 13A. Similarly, using similar concepts, referring back to FIG.13B, the liquid crystal layers 144B-1 and 144B-2 of the diffractiongrating 103B having a plurality of differently arranged diffractingregions 144B-1 a through 144B-1 g and 144B-2 a through 144B-2 g,respectively, can be fabricated.

Referring to FIGS. 15A-15C, top-down views (viewed along the x-y plane)of diffraction gratings 150A-150C according to various embodiments areillustrated. Because FIGS. 15A-15C are top down views, only the liquidcrystal layers (as opposed to the alignment layer or substrate) areillustrated, while underlying features are not shown. However, it willbe understood that the liquid crystal layer of each of the diffractiongratings 150A-150C is formed over a substrate and comprises a pluralityof diffracting zones, i.e., diffracting zones 148A-1, 148A-2, . . . and148A-n in FIG. 15A, diffracting zones 148B-1, 148B-2, . . . and 148B-nin FIG. 15B, and diffracting zones 148C-1, 148C-2, . . . and 148C-n inFIG. 15C.

The diffracting zones of each of the diffraction gratings 150A-150C havea periodically repeating lateral dimension or a grating period A andinclude corresponding liquid crystal layers formed of liquid crystalmolecules 112. The lateral dimension or the grating A can be similar tothose described above with respect to FIGS. 10A-10C.

Analogous to FIGS. 10A-10C, the diffracting zones 148A-1, 148A-2, . . .148A-n of the diffraction grating 150A have corresponding liquid crystallayers 156A-1, 156A-2, . . . 156A-n, respectively; diffracting zones148B-1, 148B-2, . . . 148B-n of the diffraction grating 150B havecorresponding liquid crystal layers 156B-1, 156B-2, . . . 156B-n,respectively; and diffracting zones 148C-1, 148C-2, . . . 148C-n of thediffraction grating 150C have corresponding liquid crystal layers156C-1, 156C-2 and 156C-n, respectively. The number of each type ofdiffracting zones can be similar to those described above with respectto FIGS. 10A-10C. In addition, the diffracting zones as arranged canperiodically repeat any suitable number of times.

Each of the liquid crystal layers 156A-1, 156A-2 and 156A-n of thediffraction grating 150A in turn has differently arranged first andsecond diffracting regions 156A-1L and 156A-1R, 156A-2L and 156A-2R, . .. and 156A-nL and 156A-nR, respectively. Similarly, each of the liquidcrystal layers 156B-1, 156B-2 and 156B-n of the diffraction grating 150Bin turn has differently arranged first and second diffracting regions156B-1L and 156B-1R, 156B-2L and 156B-2R, . . . and 156B-nL and 156B-nR,respectively. Similarly, each of the liquid crystal layers 156C-1,156C-2 and 156C-n of the diffraction grating 150C in turn hasdifferently arranged first and second diffracting regions 156C-1L and156C-1R, 156C-2L and 156C-2R, . . . and 156C-nL and 156C-nR,respectively.

Analogous to the diffraction gratings 100A-100C described above withrespect to FIGS. 10A-10C, each of the different diffracting zonesfurther comprises an alignment layer (not shown) interposed between thesubstrate and the corresponding liquid crystal layer. That is, while notshown for clarity, interposed between the substrate 104 and differentlyarranged first/second diffracting regions 156A-1L/156A-1R,156A-2L/156A-2R, . . . and 156A-nL/156A-nR of the diffraction grating150A of FIG. 15A are first and second alignment layers 160A-1L/160A-1R,160A-2L/160A-2R, . . . and 160A-nL/160A-nR, respectively. Similarlyinterposed between the substrate 104 and differently arrangedfirst/second diffracting regions 156B-1L/156B-1R, 156B-2L/156B-2R, . . .and 156B-nL/156B-nR of the diffraction grating 150C of FIG. 15B arefirst/second alignment layers 160B-1L/160B-1R, 160B-2L/160B-2R, . . .and 160B-nL/160B-nR, respectively. Similarly, interposed between thesubstrate 104 and differently arranged first/second diffracting regions156C-1L/156C-1R, 156C-2L/156C-2R, . . . and 156C-nL/156C-nR of thediffraction grating 150C of FIG. 15C are first/second alignment layers160C-1L/160C-1R, 160C-2L/160C-2R, . . . and 160C-nL and 160C-nR,respectively.

Still referring to FIGS. 15A-15C, each zone of the diffraction gratings150A, 150B and 150C include first and second regions that alternate inthe x-direction. Each of the first regions 156A-1L, 156A-2L, . . . and156A-nL of the diffraction grating 150A, each of the first regions156B-1L, 156B-2L, . . . and 156B-nL of the diffraction grating 150B andeach of the first regions 156C-1L, 156C-2L, . . . and 156C-nL of thediffraction grating 150C have liquid crystal molecules 112 that arealigned substantially along the same first alignment direction and havean azimuthal angle φ that is substantially the same. In contrast, eachof the second regions 156A-1R, 156A-2R, . . . and 156A-nR of thediffraction grating 150A, each of the second regions 156B-1R, 156B-2R, .. . and 156B-nL of the diffraction grating 150B and each of the secondregions 156C-1R, 156C-2R, . . . and 156A-nR of the diffraction grating150C have liquid crystal molecules 112 that are aligned substantiallyalong a second alignment direction different from the first alignmentdirection and have a second azimuthal angle φ that is different, e.g.,smaller, than the first azimuthal angle φ of the respective firstregions.

In each of the diffraction gratings 150A-150C of FIGS. 15A-15C,respectively, at least some of the diffracting zones have liquid crystallayers formed of liquid crystal molecules that are spatially arrangeddifferently, e.g., have azimuthal angles that are different from eachother (FIGS. 15A and 15C), or have different duty cycles that aredifferent from each other (FIGS. 15B and 15C), such that the diffractingzones have different optical properties, e.g., different refractiveindices and/or different diffraction efficiencies, according toembodiments.

In particular, referring to diffraction grating 150A of FIG. 15A, inaddition to having alignment directions and azimuthal angles φ that aredifferent from the first azimuthal angle φ of the first regions 156A-1L,156A-2L, . . . and 156A-nL, the liquid crystal molecules of the secondregions 156A-1R, 156A-2R, . . . and 156A-nR are aligned along secondalignment directions that are different from each other. For example, inthe illustrated embodiment, the zones 148A-1, 148A-2 and 148A-n arearranged such that the first regions and second regions alternate in thex-direction, where each of the first regions 156A-1L, 156A-2L, . . . and156A-nL has substantially the same azimuthal angle φ, while the secondregions 156A-1R, 156A-2R, . . . and 156A-nR have azimuthal angles φ thatare different from each other. By way of example, the first regions156A-1L, 156A-2L, . . . and 156A-nL have a an azimuthal angles φ that isbetween about 0 and about 15 degrees or between about 0 and 10 degrees,for instance 0 degrees. The second regions 156A-1R, 156A-2R, . . . and156A-nR can have azimuthal angles φ that are different from each other,where each can be between about 75 degrees and about 90 degrees, forinstance about 90 degrees; between about 60 degrees and about 90 degreesor between about 65 degrees and about 85 degrees, for instance about 75degree; between about 30 degrees and about 60 degrees or between about35 degrees and about 55 degrees, for instance about 45 degrees; betweenabout 10 degrees and about 40 degrees or between about 15 degrees andabout 35 degrees, for instance about 25 degrees.

Still referring to FIG. 15A, in some embodiments, as illustrated, thesecond regions 156A-1R, 156A-2R, . . . and 156A-nR can have azimuthalangles φ that vary, e.g., increase or decrease in one direction in alateral direction, such that a gradient in diffraction properties iscreated. In other embodiments, the second regions 156A-1R, 156A-2R, . .. and 156A-nR can have azimuthal angles φ that do not vary in onedirection in the lateral direction.

Still referring to FIG. 15A, the duty cycle can be between about 10% andabout 30%, between about 30% and about 50%, between about 50% and about70% or between about 70% and about 90%, which in the illustratedembodiment is substantially constant in the x-direction.

Referring now to FIG. 15B, as discussed above, the diffraction grating150B share some common features as the diffraction grating 150A of FIG.15A. However, unlike the diffracting grating 150B of FIG. 15A, while theliquid crystal molecules of different second regions 156B-1R, 156B-2R, .. . and 156B-nR have azimuthal angles φ that are different from thefirst azimuthal angle φ of the first regions 156B-1L, 156B-2L, . . . and156B-nL, they are not aligned differently from each other. For example,in the illustrated embodiment, the zones 148B-1, 148B-2 and 148B-n arearranged such that the first regions and second regions alternate in thex-direction, where each of the first regions 156B-1L, 156B-2L, . . . and156B-nL has substantially the same first azimuthal angle φ, and each ofthe second regions 156B-1R, 156B-2R, . . . and 156B-nR has substantiallythe same second azimuthal angle φ. The first and second azimuthal anglesof the first and second regions can have any of the values discussedabove with respect to the diffraction grating 150A of FIG. 15A.

However, unlike the grating 150A of FIG. 15A, the zones 148B-1, 148B-2and 148B-3 have substantially the same azimuthal angle, e.g., betweenabout 0 to 50 degrees, while having substantially different duty cycles,e.g., between about 40% and about 60%, for instance about 50%; betweenabout 30% and about 50%, for instance about 40% and a duty cycle betweenabout 20% and about 40%, for instance about 30%, respectively, such thatthe diffraction grating 150B has spatially varying optical properties.

Still referring to FIG. 15B, in some embodiments, as illustrated, thezones can have duty cycles that vary, e.g., increase or decrease in onedirection in a lateral direction, such that a gradient in opticalproperties is created. In other embodiments, the duty cycles do not varyin one direction in the lateral direction.

Referring now to FIG. 15C, the illustrated diffraction grating 150Ccombines features similar to those described above with respect to thediffraction gratings 150A and 150B of FIGS. 15A and 15B. In particular,the liquid crystal molecules of different second regions 156C-1R,156C-2R, . . . and 156C-nR can have azimuthal angles φ that aredifferent from the first azimuthal angles φ of the first regions116C-1L, 116C-2L, . . . and 116C-nL, and different from each other. Inaddition, the duty cycle varies between adjacent zones across a lateraldirection, e.g., x-direction. The first and second azimuthal angles ofthe first and second regions can have any of the values discussed abovewith respect to the diffraction grating 150A of FIG. 15A. In addition,the duty cycle variation between adjacent zones across a lateraldirection, e.g., x-direction, can also have values discussed above withrespect to the diffraction grating 150B of FIG. 15B.

Referring now to FIG. 16A, a top-down view (x-y plane) of a diffractiongrating 160 according to some other embodiments are illustrated, inwhich azimuthal angles of liquid crystal molecules rotate across alateral length of a zone. The diffraction grating having sucharrangement is sometimes referred a polarization grating. While notshown for clarity, the diffraction grating 160 comprises a substrate andan alignment layer formed thereon, and a plurality of differentlyarranged diffracting zones 164-1 and 164-2. The diffracting zones 164-1and 164-2 have corresponding liquid crystal layers 168-1 and 168-2,respectively. Each of the liquid crystal layers liquid crystal layers168-1 and 168-2 of the diffraction grating 160 in turn has a pluralityof differently arranged diffracting regions 168-1 a to 168-1 i and 168-2a to 168-2 i, respectively. Each of the plurality of regions 168-1 a to168-1 i of the zone 164-1 and each of the plurality of regions 168-2 ato 168-2 i of the zone 164-2 has liquid crystal molecules 112 that arealigned substantially along the same alignment direction within the sameregion. Thus, it will be understood that, each of the zones include astack of liquid crystal molecules stacked in the z-direction.

The liquid crystal molecules 112 of each of the diffracting regions168-1 a to 168-1 i of the zone 164-1 and regions 168-2 a to 168-2 i ofthe zone 164-2 have substantially the same azimuthal angle φ within thesame region. However, the liquid crystal molecules 112 of differentdiffracting regions have substantially different azimuthal angles. Inaddition, the liquid crystal molecules 112 of different diffractingregions can have substantially the same or different pre-tilt angle Φ,similar to as described above with respect to FIGS. 13A and 13B.

In the illustrate embodiment, the liquid crystal molecules 112 of eachof the diffracting regions 168-1 a to 168-1 i of the zone 164-1 and thecorresponding regions 168-2 a to 168-2 i of the zone 164-2 havesubstantially the same azimuthal angle φ within the same region.However, distances between adjacent regions are substantially differentbetween the zone 164-1 and the zone 164-2, such that spatially varyingdiffraction properties are generated, as illustrated in reference toFIG. 16B. Referring to FIG. 16B, a graph 162 schematically showing theazimuthal angle φ as a function of a lateral position x for thediffraction grating 160 in FIG. 16A is illustrated. The x-axisrepresents a lateral distance in the x-direction and the y-axisrepresents the azimuthal angle φ. The curves 162-1 and 162-1 representthe azimuthal angle φ as a function of the lateral position x for thezone 164-1 and the zone 164-2, respectively.

Referring back to FIG. 16A, the liquid crystal molecules 112 of thediffracting region 164-1 are arranged such that the rate of change inazimuthal angle φ per a unit of lateral length, i.e., Δφ/Δx in thex-direction, is relatively constant, as illustrated by the curve 162-1of FIG. 16B. In contrast, the liquid crystal molecules 112 of thediffracting region 164-2 are arranged such that the Δφ/Δx in thex-direction varies substantially across x, as illustrated by the curve162-2 of FIG. 16B. As a result, the curve 162-2 is characterized by acentral region of the zone 164-2 in which the Δφ/Δx varies relativelyslowly and end regions of the zone 164-2 in which the Δφ/Δx variesrelatively rapidly. As a result, the diffraction properties (includingefficiencies and refractive indices) differ from those of the gratingwith a uniform variation of its azimuthal angle of liquid crystals.

FIGS. 17A-17E illustrate a method for fabricating diffraction gratingshaving non-uniform azimuthal angles, e.g., diffraction gratings150A-150C of FIGS. 15A-15C described above, using photo-alignmenttechniques, according to embodiments. In particular, in the illustratedembodiment, the method uses multiple exposures of the alignment layersprior to deposition of the liquid crystals. In the illustrated method ofFIGS. 17A-17E, similar to the method illustrated with respect to FIGS.11A-11B, a substrate 104 is provided on which a photo-alignment layer120 is formed.

Referring to an intermediate structure 150A illustrated in FIG. 17A,after forming the photo-alignment layer 120 on the substrate 104, afirst photomask 174A is used to expose different regions of theunderlying photo-alignment layer 120 to different doses of light and/ordifferent polarizations of light. For example, different regions of thephoto-alignment layer 120 corresponds to first (e.g., left) and second(e.g., right) regions of each of the zones 148A-1 and 148A-2 asdescribed above with respect to the diffraction grating 150A in FIG.15A.

In some embodiments, the first photomask 174A can be a gray-scale maskhaving a plurality of mask regions 174A-1- to 174A-4 that are at leastpartially transparent and possibly have one or more opaque regions.Different one of the plurality of mask regions 174A-1- to 174A-4 may beconfigured to transmit different doses of a first incident light 172A,such that transmitted light 172A transmitted through different ones ofthe plurality of mask regions have varying intensities that areproportional to the relative transparency of the different mask regions.In other embodiments, the photomask 174A can be a binary mask having theplurality of mask regions 174A-1- to 174A-4 each being fully or nearlyfully transparent or fully or nearly fully opaque, such that transmittedlight 172A has binary intensities. In the illustrated example, the firstincident light 172A can be polarized, e.g., linearly polarized at afirst angle, e.g., 0 degrees, as schematically depicted by polarizationvectors 178A, and substantially transmits through the mask regions174A-1 and 174A-3 corresponding to first (e.g., left) regions of each ofthe zones 148A-1 and 148A-2 of the diffraction grating 150A asillustrated in FIG. 15A, while substantially being blocked in otherregions.

Referring to an intermediate structure 150B illustrated in FIG. 17B,after exposing different regions of the photo-alignment layer 120 to thefirst incident light 172A, a second photomask 174B is used to exposedifferent regions of the underlying photo-alignment layer 120 todifferent doses of light and/or different polarizations of light using asecond incident light 172B.

In some embodiments, the second photomask 174B can be a gray-scale maskdifferent from the first photomask 174A and having a plurality of maskregions 174B-1- to 174B-4 that are at least partially transparent andpossibly have one or more opaque regions. Different ones of theplurality of mask regions 174B-1- to 174B-4 may be configured totransmit different doses of the second incident light 172B. In otherembodiments, the photomask 174B can be a binary mask having theplurality of mask regions 174B-1- to 174B-4 each being fully or nearlyfully transparent or fully or nearly fully opaque, such that transmittedlight 172B has binary intensities. The second incident light 172B can bepolarized, e.g., linearly polarized at a second angle different, e.g.,orthogonal, from the first polarization angle of the first incidentlight 178A. For example, the second incident light 172B can beorthogonally linearly polarized relative to the first incident light172A, e.g., at 90 degrees, as schematically depicted by polarizationvectors 178B and substantially transmits through the mask region 174B-2corresponding to a second (e.g., right) region of the zone 148A-1 of thediffraction grating 150A illustrated in FIG. 15A, while substantiallybeing blocked in other regions.

Referring to an intermediate structure in FIG. 17C, after exposingdifferent regions of the photo-alignment layer 120 to the secondincident light 172B, a third photomask 174C is used to expose differentregions of the underlying photo-alignment layer 120 to different dosesof light and/or different polarizations of light using a third incidentlight 172C.

In some embodiments, the third photomask 174C can be a gray-scale maskdifferent from the first and second photomasks 174A, 174B and having aplurality of mask regions 174C-1- to 174C-4 that are at least partiallytransparent and possibly have one or more opaque regions. Different onesof the plurality of mask regions 174C-1- to 174C-4 may be configured totransmit different doses of the third incident light 172C. In otherembodiments, the photomask 174C can be a binary mask having theplurality of mask regions 174C-1- to 174C-4 each being fully or nearlyfully transparent or fully or nearly fully opaque, such that transmittedlight 172C has binary intensities. The third incident light 178C can bepolarized, e.g., linearly polarized at a third angle different from thefirst and second polarization angles of the first and second incidentlights 178A and 178B. In the illustrated embodiment, the third incidentlight 172C is linearly polarized at 45 degrees, as schematicallydepicted by polarization vectors 178C and substantially transmitsthrough the mask region 174A-4 corresponding to a second (e.g., right)region of the zone 148A-2 of the diffraction grating 150A illustrated inFIG. 15A, while substantially being blocked in other regions.

Referring to FIGS. 17D (cross-sectional view) and 17E (top-down view),after exposing different regions of the photo alignment layer 120through the multi-exposure process described above with respect to FIGS.17A-17C, a liquid crystal layer can be deposited on the photo alignmentlayer 120. As a result of the different doses and/or polarizations oflight received by different regions of the photo alignment layer 120,differently configured liquid crystal layers 156A-1 and 156A-2 areformed in respective zones 148A-1 and 148A-2, respectively. The liquidcrystal layers 156A-1 and 156A-2 have first and second diffractingregions 156A-1L and 156A-1R and 156A-2L and 156A-2R, respectively. Asdescribed above with respect to FIG. 15A, the first regions and secondregions alternate in the x-direction, where each of the first regions156A-1L and 156A-2L has substantially the same first azimuthal angle φ,while the second regions 156A-1R and 156A-2R have azimuthal angles φthat are different from each other and from the first azimuthal angle ofthe first regions. Without being bound to any theory, in some cases,exposure of the underlying photo-alignment layer 120 to light havingdifferent polarization angles leads to different azimuthal angles of theliquid crystal molecules.

Still referring to FIGS. 17D and 17E, the azimuthal angle φ of theliquid crystal molecules can be determined by the linear polarizationangle of the exposure light and the type of photo-alignment layer 120.In the illustrated embodiment, the photo-alignment layer 120 isconfigured such that the degree of rotation of the liquid crystalmolecules, as measured by an absolute value the azimuthal angle φ up to+/−90 degrees, is determined by the linear polarization orientationangle of transmitted light received by the underlying alignment layer upto +/−90 degrees. In some embodiments, such as the illustratedembodiment, the photo-alignment layer 120 can be configured such thatthe liquid crystal molecules are oriented substantially parallel to thepolarization direction of the exposure light (e.g., the azimuthal angleφ and the linear polarization angle of the exposure light aresubstantially the same). Embodiments are not so limited, however, and inother embodiments, the photo-alignment layer 120 can be configured suchthat the liquid crystal molecules are oriented substantially orthogonalto the polarization direction of the exposure light (e.g., the azimuthalangle φ and the linear polarization angle of the exposure light aresubstantially offset by about +/−90 degrees). For example, in theillustrated embodiment, the photo-alignment layers 160A-1L and 160A-2Lreceive light with the same linear polarization orientation and thephoto alignment layer 160A-1R receives light with the larger differencein linear polarization orientation angle with respect to the linearpolarization orientation of the photo-alignment layers 160A-1L and160A-2L, followed by the photo alignment layer 160A-2R. As a result, theresulting azimuthal angles are the same for the first regions 156A-1Land 156A-2L and the difference in the resulting azimuthal angles withrespect to the first regions 156A-1L and 156A-2L is larger for thesecond region 156A-1R than that for the second region 156A-2R

In various embodiments described herein, photomasks can comprise linearpolarizers such as wire-grid polarizers having a regular array ofparallel metallic wires placed in a plane perpendicular to the directionof propagation of the incident light. In some embodiments describedherein, the photomasks may be configured to provide illumination havinguniform polarization angle across the photo-alignment layer. Whencomprising wire-grid polarizers, these embodiments may be realized byconfiguring the array of metallic wires to be uniform across thephotomasks, e.g., uniform in the thickness and/or the density of themetallic wires. In other embodiments, the photomasks may be configuredto provide illumination having non uniform or having multiplepolarization angles across different regions of the photo-alignmentlayer. When comprising wire-grid polarizers, these embodiments may berealized by configuring the array of metallic wires to be nonuniform andvarying across the photomasks, e.g., nonuniform and varying in thethickness and/or the density of the metallic wires. Thus, varying thethickness and density of metallic wires, both the polarization angle andthe transmittance of the light can be controlled, according to variousembodiments.

FIGS. 18A-18D illustrate another method for fabricating a diffractiongrating 160 according to some other embodiments, in which azimuthalangles of liquid crystal molecules rotate across a lateral length of azone, e.g., polarization grating. In particular, in the illustratedembodiment, the method uses polarization interference holographicexposure using a gray-scale mask, according to embodiments.

Referring to FIG. 18A showing an intermediate structure 160A, in theillustrated method, processes leading up to forming the photo-alignmentlayer 120 to UV light is similar to the method described above withrespect to FIGS. 17A-17E. Thereafter, a plurality of coherent lightbeams 182A, 182B having different polarizations are directed to theplurality of differently arranged diffracting zones 164A-1 and 164A-2.In the illustrated embodiment, the light beams 182A and 182B includeorthogonal circular polarized light beams. However, the light beams 182Aand 182B can include elliptical polarized light beams, for example. Inthe illustrated embodiment, both zones 164-1 and 164-2 are unmasked.

Thereafter, referring to FIG. 18B showing an intermediate structure160B, a photomask 184 is used to expose different zones of theunderlying photo-alignment layer 120 to different doses of light and/ordifferent polarizations of light using a linearly polarized incidentlight 188 having any polarization angle discussed above with respect toFIGS. 17A-17E. For example, different zones of the photo-alignment layer120 may correspond to the zones 164-1 and 164-2 as described above withrespect to the diffraction grating 160 in FIG. 16B. As a result of thesecondary exposure to linearly polarized light 188, a fraction of thephoto-alignment layer 120 can be realigned. Without being bound to anytheory, when the photo-alignment layer 120 is exposed twice withdifferent linear polarization orientations, the orientations of theliquid crystal molecules can be determined by the relative linearpolarization orientations and the exposure doses of two exposures.

Referring now to FIGS. 18C and 18D, a cross-sectional view (x-z plane)and a top-down view (x-y plane) of the diffraction grating 160corresponding to that in FIG. 16B is illustrated. At least in part as aresult of the first and second exposures as described above with respectto FIGS. 18A and 18B, liquid crystal layers 168-1 and 168-2 having aplurality of differently arranged diffracting regions 168-1 a to 168-1 iand 168-2 a to 168-2 i are generated, respectively. Each of theplurality of regions 168-1 a to 168-1 i of the zone 164-1 and each ofthe plurality of regions 168-2 a to 168-2 i of the zone 164-2 has liquidcrystal molecules 112 that are aligned substantially along the samealignment direction within the same region. Thus, it will be understoodthat, each of the zones include a stack of liquid crystal moleculesstacked in the z-direction.

Spatially Variable Liquid Crystal Diffraction Gratings Based onSpatially Varying Liquid Crystal Materials

In various embodiments discussed supra, the liquid crystal molecules arefabricated using photo-alignment techniques. However, other embodimentsare possible, which can be fabricated with or without photo-alignment.

Referring to FIGS. 19A and 19B, top-down (viewed along the x-y plane)and side (viewed along the x-z plane) views of a diffraction grating190, which can be fabricated with or without photo-alignment, accordingto some embodiments are illustrated. The diffraction grating 190comprises a plurality of diffracting zones, i.e., diffracting zones198-1, 198-2, . . . and 198-n that have a periodically repeating lateraldimension or a grating period A and include corresponding liquid crystallayers formed of liquid crystal molecules 112. The lateral dimension orthe grating period A can be similar to those described above withrespect to FIGS. 10A-10C.

The diffracting zones 198-1, 198-2, . . . 198-n of the diffractiongrating 190 have corresponding liquid crystal layers 186-1, 186-2, . . .186-n, respectively. The number of each type of diffracting zones can besimilar to those described above with respect to FIGS. 10A-10C. Inaddition, the diffracting zones as arranged can periodically repeat anysuitable number of times. Each of the liquid crystal layers 186-1, 186-2and 186-n of the diffraction grating 190 in turn has differentlyarranged first and second diffracting regions 186-1L and 186-1R, 186-2Land 186-2R, . . . and 186-nL and 186-nR, respectively.

The different liquid crystal layers 186-1, 186-2 and 186-n have liquidcrystal molecules 112 that are arranged to have different degrees ofchirality. As described above, chirality can be described by a chiralpitch, p, which can refer to the distance over which the liquid crystalmolecules undergo a full 360° twist. The chirality can also becharacterized by a twist deformation angle, which is an angle of twistthe liquid crystal molecules undergo within a thickness of the liquidcrystal layer. For example, in the illustrated embodiment, the firstliquid crystal layer 186-1 has the first and second diffracting regions186-1L and 186-1R that have liquid crystal molecules 112 havingdifferent azimuthal angles with little or no chirality (very large orinfinite chiral pitch p). The second and third liquid crystal layers186-2 and 186-n have respective first/second diffracting regions186-2L/186-2R and 186-nL/186-nR, respectively, that have liquid crystalmolecules 112 having substantial and substantially different degrees ofchirality. Similarly, in various embodiments, the azimuthal angles of orthe difference in azimuthal angles between the uppermost liquid crystalmolecules in the first and second diffracting regions 186-2L/186-2R and186-nL/186-nR of the second and nth liquid crystal layers 186-2 and186-n, respectively, can be any value described above with respect tothe diffraction gratings 150A-150C in FIGS. 15A-15C

In some embodiments, each pair of first/second diffracting regionswithin a zone, e.g., the pair of regions 186-2L/186-2R of the zone 198-2(see FIG. 19A) and the pair of regions 186-nL/186-nR of the zone 198-nhave uppermost liquid crystal molecules that have different azimuthalangles φ but have the same chiral pitch p. In some other embodiments,the pairs of regions within zones have uppermost liquid crystalmolecules that have the same azimuthal angles φ but have differentchiral pitches p. In various embodiments, a chiral twist (e.g., twistangle or twist deformation angle) of the liquid crystal molecules in agiven region of the pair of regions 186-2L/186-2R of the zone 198-2 andthe pair of regions 186-nL/186-nR of the zone 198-n can be, e.g., about+/−45°, about +/−90°, about +/−135°, or about +/−180°. The correspondingchiral period p can be 8D, 4D, or 3D, where 2D is the thickness of theliquid crystal layers.

For example, in the illustrated embodiment, the uppermost liquid crystalmolecules of the first and second regions 186-2L and 186-2R have firstand second azimuthal angles φ of, e.g., 135° and 45°, respectively,while having a first chiral pitch, e.g., of about 8D, where D is thethickness of the liquid crystal layers. As a result, in each of thefirst and second regions 186-2L and 186-2R, the uppermost liquid crystalmolecule and the lowermost liquid crystal molecule are twisted relativeto each other by about −45 degrees. In addition, in the illustratedembodiment, the uppermost liquid crystal molecules of the first andsecond regions 186-nL, 186-nR have third and fourth azimuthal angles φof, e.g., 90° and 0°, respectively, while having a second chiral pitchof about 4D, where D is the thickness of the liquid crystal layers. As aresult, in each of the first and second regions 186-nL and 186-nR, theuppermost liquid crystal molecule and the lowermost liquid crystalmolecule are twisted relative to each other by about −90 degrees.However, the azimuthal angles φ of uppermost liquid crystal molecules ofthe first/second diffracting regions 186-2L/186-2R and 186-nL/186-nR canhave any value such as described above with respect to FIG. 15A-15C.

Still referring to FIGS. 19A and 19B, in some embodiments, the liquidcrystal molecules 112 in each region have the same pre-tilt angle Φ,which can be zero or higher.

Still referring to FIGS. 19A and 19B, the duty cycle of different liquidcrystal layers 186-1, 186-2 and 186-n, can be different, and each can bebetween about 10% and about 30%, between about 30% and about 50%,between about 50% and about 70% or between about 70% and about 90%.

Referring now to FIG. 20, cross-sectional side (x-z plane) view of adiffraction grating 200 according to some other embodiments areillustrated. While not shown for clarity, the diffraction grating 200comprises a substrate and a plurality of differently arrangeddiffracting zones 208-1 and 208-2 having corresponding liquid crystallayers 196-1 and 196-2, respectively. Each of the liquid crystal layersliquid crystal layers 196-1 and 196-2 of the diffraction grating 200 inturn has a plurality of differently arranged diffracting regions 196-1 athrough 196-1 g and 196-2 a through 196-2 g, respectively.

Similar to liquid crystal molecules 112 of the liquid crystal layer186-1 of FIGS. 19A/19B, the liquid crystal molecules 112 of thediffracting regions 196-1 a through 196-1 g of the liquid crystal layer196-1 illustrated in FIG. 20 has different azimuthal angles but littleor no chirality (very large or infinite chiral pitch p) from layer tolayer. The azimuthal angles and other arrangements of adjacentdiffracting regions 196-1 a through 196-1 g are similar to thosedescribed with respect to the first and second diffracting regions186-1L and 186-1R with respect to FIGS. 19A/19B.

Similar to liquid crystal molecules 112 of the liquid crystal layers186-2 and 186-n of FIGS. 19A/19B, the liquid crystal molecules 112 ofthe diffracting regions 196-2 a through 196-2 g of the liquid crystallayer 196-2 illustrated in FIG. 20 have substantial and substantiallydifferent degrees of chirality along the length of the zone (along the xdirection), and have uppermost liquid molecules that have differentazimuthal angles. The azimuthal angles, the chirality and otherarrangements of adjacent diffracting regions 196-2 a through 196-2 g aresimilar to those described with respect to the first and seconddiffracting regions 186-2L/186-2R and 186-nL/186-nR of the second andnth liquid crystal layers 186-2 and 186-n.

It will be appreciated that, when a twist is induced to liquid crystalmolecules as illustrated above with respect to FIGS. 19A/19B and 20, theresulting diffraction grating exhibits spatially varying diffractionproperties, including refractive index and diffraction efficiencies.Some liquid crystal molecules can be made chiral by substituting one ormore of the carbon atoms asymmetrically by four different ligands. Otherliquid crystal molecules can be made chiral by adding mesogenic ornon-mesogenic chiral dopants at varying concentration to one of liquidcrystal phases described above. According to embodiments, by addingsmall concentrations, including, for example, but not limited to below5%-10% by weight, chirality related effects can be increased with theconcentration of the dopant. Some examples of chiral liquid crystalmolecules include cholesteryl-benzoate, a ferroelectric liquid crystalN(p-n-Decyloxybenzylidene) p-amino 2-methylbutyl cinnamate (DOBAMBC),and achiral MBBA (4-butyl-N-[4-methoxy-benzylidene]-aniline), which is aroom temperature nematic, doped with chiral R1011. Other chiral liquidcrystal molecules may be used.

Referring to FIG. 21, a side view (viewed along the x-z plane) of adiffraction grating 210, which can be fabricated with or withoutphoto-alignment, according to some embodiments are illustrated. Thediffraction grating 210 comprises a plurality of diffracting zones,i.e., diffracting zones 218-1, 218-2, . . . and 218-n that have aperiodically repeating lateral dimension or a grating period A in asimilar manner to those described above with respect to FIGS. 10A-10C.The diffracting zones 218-1, 218-2, . . . and 218-n of the diffractiongrating 210 have corresponding liquid crystal layers 206-1, 206-2, . . .and 206-n, respectively. The number of each type of diffracting zonescan be similar to those described above with respect to FIGS. 10A-10C.In addition, the diffracting zones as arranged can periodically repeatany suitable number of times.

In the diffraction grating 210, different liquid crystal layers 206-1,206-2 and 206-n comprise different liquid crystal materials. Inparticular, first and second diffracting regions 206-1L and 206-1R,206-2L and 206-2R, . . . and 206-nL and 206-nR have liquid crystalmolecules 212-1L and 212-1R, 212-2L and 212-2R, . . . and 212-nL and212-nR, respectively which can be the same or different liquid crystalmolecules. For example, in some implementations, regions within a firstzone can have a first liquid crystal material, regions within a secondzone can have a first liquid crystal material and regions within a thirdzone can have a third liquid crystal material. In other implementations,any given zone can have a first region having a first liquid crystalmaterial and a second region having a second liquid crystal material.Accordingly, the optical properties can be changed along the length ofthe diffraction grating by changing the composition of the material, forexample, using the same host material with different level of the samedopant (or with different dopants with same or different levels), andnot necessary changing the orientation of the liquid crystal molecules.

In some embodiments, different zones have different liquid crystalmolecules while other aspects of the liquid crystal orientation, e.g.,the tilt angle, the azimuthal angle, and chirality as described aboveare similar or the same between different zones. In some otherembodiments, different zones have different liquid crystal moleculeswhile having other aspects of the liquid crystal orientation, e.g., thetilt angle, the azimuthal angle, and chirality that are also different,as discussed supra in the context of various embodiments.

By depositing different liquid crystal materials during deposition or bymodifying the liquid crystal material after deposition, localbirefringence can be controlled to be different across different zones.In various embodiments, birefringence of individual zones can be betweenabout 0.05 and about 0.15, for instance about 0.10, between about 0.15and about 0.25, for instance about 0.2, and between about 0.25 and about0.35, for instance about 0.3.

Additional Examples

In a 1^(st) example, a diffraction grating includes a plurality ofdifferent diffracting zones having a periodically repeating lateraldimension corresponding to a grating period adapted for lightdiffraction. The diffraction grating additionally includes a pluralityof different liquid crystal layers corresponding to the differentdiffracting zones. The different liquid crystal layers have liquidcrystal molecules that are aligned differently, such that the differentdiffracting zones have different optical properties associated withlight diffraction.

In a 2^(nd) example, in the diffraction grating of the 1^(st) example,the optical properties include one or more of refractive index,absorption coefficient, diffraction efficiency and birefringence.

In a 3^(rd) example, in the diffraction grating of any of the 1^(st) to2^(nd) examples, each of the different liquid crystal layers has aplurality of differently arranged regions, wherein the differentlyarranged regions have liquid crystal molecules that are aligneddifferently with respect to each other.

In a 4^(th) example, in the diffraction grating of any of the 1^(st) to3^(rd) examples, each of the different diffracting zones furthercomprises an alignment layer interposed between a substrate and thecorresponding liquid crystal layer, wherein different alignment layersbetween the different diffracting zones and the substrate are formed ofthe same material composition, said different alignment layers causingthe liquid crystal molecules to be aligned differently in the differentdiffracting zones.

In a 5^(th) example, in the diffraction grating of any of the 1^(st) to4^(th) examples, the liquid crystal molecules comprise calamitic liquidcrystal molecules that are elongated and aligned along an elongationdirection.

In a 6^(th) example, in the diffraction grating of any of the 1^(st) to5^(th) examples, the different liquid crystal layers include a firstregion and a second region, wherein liquid crystal molecules of thefirst region are aligned along a first alignment direction which forms afirst alignment angle with respect to a reference direction, and whereinliquid crystal molecules of the second region are aligned along a secondalignment direction which forms a second alignment angle with respect tothe reference direction, the second alignment angle different from thefirst alignment angle.

In a 7^(th) example, in the diffraction grating of the 6^(th) example,liquid crystal molecules of a first region of a first liquid crystallayer and liquid crystal molecules of a corresponding first region of asecond liquid crystal layer have substantially the same alignment angle.

In an 8^(th) example, in the diffracting grating of the 7^(th) example,liquid crystal molecules of a second region of the first liquid crystallayer and liquid crystal molecules of a corresponding second region ofthe second liquid crystal layer have different alignment angles.

In a 9^(th) example, in the diffraction grating of the 6^(th) example,liquid crystal molecules of a first region of a first liquid crystallayer and the liquid crystal molecules of a corresponding first regionof a second liquid crystal layer have substantially different alignmentangles, and wherein liquid crystal molecules of a second region of thefirst liquid crystal layer and liquid crystal molecules of acorresponding second region of the second liquid crystal layer havedifferent alignment angles.

In a 10^(th) example, in the diffraction grating of the 6^(th) example,a ratio of lateral widths between first regions and second regions issubstantially the same between different zones.

In an 11^(th) example, in the diffraction grating of the 6^(th) example,liquid crystal molecules of a second region of a first liquid crystallayer and liquid crystal molecules of a second region of a second liquidcrystal layer have substantially same alignment angles, and wherein aratio of lateral widths between the first regions and the second regionsis substantially different between different zones.

In a 12^(th) example, in the diffraction grating of the 6^(th) example,liquid crystal molecules of a second region of a first liquid crystallayer and liquid crystal molecules of a second region of a second liquidcrystal layer have different alignment angles, and wherein a ratio oflateral widths between the first regions and the second regions issubstantially different between different zones.

In a 13^(th) example, in the diffracting grating of the 6^(th) example,the first and second alignment angles are pre-tilt angles that aremeasured in a plane perpendicular to a major surface of a substrate andbetween respective alignment directions and the major surface.

In a 14^(th) example, in the diffraction grating of the 6^(th) example,the first and second alignment angles are azimuthal angles that aremeasured in a plane parallel to a major surface of the substrate andbetween respective alignment directions and a reference directionparallel to the major surface.

In a 15^(th) example, in the diffraction grating of the 3^(rd) example,the different liquid crystal layers include a first region and a secondregion, wherein liquid crystal molecules of the first region are alignedalong a plurality of first alignment directions which forms a pluralityof first alignment angles with respect to a reference direction, andwherein liquid crystal molecules of the second region are aligned alonga plurality of second alignment directions which forms a plurality ofsecond alignment angles with respect to the reference direction.

In a 16^(th) example, in the diffraction grating of any of the 1^(st) to15^(th) examples, the diffraction grating is a transmissive diffractiongrating having a transparent substrate.

In a 17^(th) example, in the diffraction grating of any of the 1^(st) to16^(th) examples, different diffracting zones comprise differentmaterial compositions such that the different diffracting zones havedifferent optical properties associated with light diffraction.

In an 18^(th) example, a method of fabricating a diffraction gratingincludes providing a substrate. The method additionally includesproviding a plurality of different diffracting zones having aperiodically repeating lateral dimension corresponding to a gratingperiod adapted for light diffraction. The method further includesforming a plurality of different liquid crystal layers comprising liquidcrystal molecules over the substrate, the different liquid crystallayers corresponding to the different diffracting zones, wherein formingthe different liquid crystal layers comprises aligning the liquidcrystal molecules differently, thereby providing different opticalproperties associated with light diffraction to the differentdiffracting zones.

In a 19^(th) example, in the method of the 18^(th) example, the methodfurther includes forming a photo-alignment layer on the substrate priorto forming the liquid crystal layers and illuminating thephoto-alignment layer thereby causing the liquid crystal moleculesformed on the alignment layer to be aligned differently in the differentdiffracting zone.

In a 20^(th) example, in the method of the 19^(th) example, forming thephoto-alignment layer includes depositing a material selected from thegroup consisting of polyimide, linear-polarization photopolymerizablepolymer, azo-containing polymers, courmarine-containing polymers,cinnamate-containing polymers and combinations thereof.

In a 21^(st) example, in the method of any of the 19^(th) and 20^(th)examples, the method further includes, after forming the photo-alignmentlayer and prior to forming the liquid crystal layers, exposing thedifferent diffracting zones to different doses of light using a grayscale mask.

In a 22^(nd) example, in the method of any of 19^(th) to 21^(st)examples, forming the different liquid crystal layers includes forming aplurality of differently arranged regions in the different liquidcrystal layers, wherein the differently arranged regions have liquidcrystal molecules that are aligned differently with respect to eachother.

In a 23^(rd) example, in the method of the 22^(nd) example, forming thedifferent liquid crystal layers comprises forming a first region and asecond region, wherein forming the first region comprises aligningliquid crystal molecules of the first region along a first alignmentdirection which forms a first alignment angle with respect to areference direction, and wherein forming the second region comprisesaligning liquid crystal molecules of the second region along a secondalignment direction which forms a second alignment angle with respect tothe reference direction, wherein the second alignment angle differentfrom the first alignment angle.

In a 24^(th) example, in the method of the 23^(rd) example, aligning theliquid molecules of the first and second regions includes forming therespective first and second alignment angles that are inverselyproportional to the different doses of light.

In a 25^(th) example, in the methods of any of the 18^(th) to 24^(th)examples, forming the plurality of different liquid crystal layerscomprises inducing chirality in at least some of the liquid crystalmolecules by adding a chiral dopant to the liquid crystal layers.

In a 26^(th) example, in the method of the 18^(th) example, forming thedifferent liquid crystal layers includes forming a first region and asecond region in the liquid crystal layers, wherein liquid crystalmolecules of the first region are aligned along a plurality of firstalignment directions which forms a plurality of first alignment angleswith respect to a reference direction, and wherein liquid crystalmolecules of the second region are aligned along a plurality of secondalignment directions which forms a plurality of second alignment angleswith respect to the reference direction.

In a 27^(th) example, a diffraction grating includes a plurality ofcontiguous liquid crystal layers extending in a lateral direction andarranged to have a periodically repeating lateral dimension, a thicknessand indices of refraction such that the liquid crystal layers areconfigured to diffract light. Liquid crystal molecules of the liquidcrystal layers are arranged differently in different liquid crystallayers along the lateral direction such that the contiguous liquidcrystal layers are configured to diffract light with a gradient indiffraction efficiency.

In a 28^(th) example, in the diffraction grating of the 27^(th) example,the liquid crystal layers have a first region and a second region, andwherein the contiguous liquid crystal layers are arranged such that aplurality of first regions and a plurality of second regions alternatein the lateral direction.

In a 29^(th) example, in the diffraction grating of the 28^(th) example,the liquid crystal molecules in the first regions have substantially thesame alignment orientation, whereas the liquid crystal molecules in thesecond regions are have substantially different alignment directions.

In a 30^(th) example, a head-mounted display device is configured toproject light to an eye of a user to display augmented reality imagecontent. The head-mounted display device includes a frame configured tobe supported on a head of the user. The head-mounted display deviceadditionally includes a display disposed on the frame, at least aportion of said display comprising one or more waveguides, said one ormore waveguides being transparent and disposed at a location in front ofthe user's eye when the user wears said head-mounted display device suchthat said transparent portion transmits light from a portion of anenvironment in front of the user to the user's eye to provide a view ofsaid portion of the environment in front of the user, said displayfurther comprising one or more light sources and at least onediffraction grating configured to couple light from the light sourcesinto said one or more waveguides or to couple light out of said one ormore waveguides. The diffraction grating includes a plurality ofdifferent diffracting zones having a periodically repeating lateraldimension corresponding to a grating period adapted for lightdiffraction. The diffraction grating additionally includes a pluralityof different liquid crystal layers corresponding to the differentdiffracting zones, wherein the different liquid crystal layers haveliquid crystal molecules that are aligned differently, such that thedifferent diffracting zones have different optical properties associatedwith light diffraction.

In a 31^(st) example, in the device of the 30^(th) example, the one ormore light sources include a fiber scanning projector.

In a 32^(nd) example, in the device of any of the 30^(th) to 31^(st)examples, the display is configured to project light into the user's eyeso as to present image content to the user on a plurality of depthplanes.

In a 33^(rd) example, in the diffraction grating of any of the 30^(th)to 32^(nd) examples, the optical properties include one or more ofrefractive index, absorption coefficient, diffraction efficiency andbirefringence.

In the embodiments described above, augmented reality display systemsand, more particularly, spatially varying diffraction gratings aredescribed in connection with particular embodiments. It will beunderstood, however, that the principles and advantages of theembodiments can be used for any other systems, apparatus, or methodswith a need for the spatially varying diffraction grating. In theforegoing, it will be appreciated that any feature of any one of theembodiments can be combined and/or substituted with any other feature ofany other one of the embodiments.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including” and the like are to be construed in an inclusivesense, as opposed to an exclusive or exhaustive sense; that is to say,in the sense of “including, but not limited to.” The word “coupled”, asgenerally used herein, refers to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Likewise, the word “connected”, as generally used herein,refers to two or more elements that may be either directly connected, orconnected by way of one or more intermediate elements. Additionally, thewords “herein,” “above,” “below,” “infra,” “supra,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Detailed Description using thesingular or plural number may also include the plural or singularnumber, respectively. The word “or” in reference to a list of two ormore items, that word covers all of the following interpretations of theword: any of the items in the list, all of the items in the list, andany combination of the items in the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or whether these features,elements and/or states are included or are to be performed in anyparticular embodiment.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel apparatus, methods, andsystems described herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the disclosure. For example, while blocks arepresented in a given arrangement, alternative embodiments may performsimilar functionalities with different components and/or circuittopologies, and some blocks may be deleted, moved, added, subdivided,combined, and/or modified. Each of these blocks may be implemented in avariety of different ways. Any suitable combination of the elements andacts of the various embodiments described above can be combined toprovide further embodiments. The various features and processesdescribed above may be implemented independently of one another, or maybe combined in various ways. All suitable combinations andsubcombinations of features of this disclosure are intended to fallwithin the scope of this disclosure.

What is claimed is:
 1. A diffraction grating, comprising: a plurality ofdifferent diffracting zones arranged laterally in a lateral directionsubstantially parallel to a major surface of a substrate and having aperiodically repeating lateral dimension corresponding to a gratingperiod adapted for light diffraction; and a plurality of differentliquid crystal layers arranged differently in different diffractingzones to diffract light passing therethrough, wherein the differentliquid crystal layers have liquid crystal molecules that are aligneddifferently, wherein the different liquid crystal layers of thedifferent diffracting zones are formed in the lateral direction as acontinuous layer contacting a common surface over the substrate, andwherein the different liquid crystal layers comprise correspondingregions in which the liquid crystal molecules have substantiallydifferent alignment angles with respect to a reference direction, suchthat the different diffracting zones have different optical propertiesassociated with light diffraction.
 2. The diffraction grating of claim1, wherein the optical properties include one or more of refractiveindex, absorption coefficient, diffraction efficiency and birefringence.3. The diffraction grating of claim 1, wherein each of the differentliquid crystal layers has a plurality of differently arranged regions,wherein the differently arranged regions have liquid crystal moleculesthat are aligned differently with respect to each other.
 4. Thediffraction grating of claim 3, wherein the different liquid crystallayers include a first region and a second region, wherein liquidcrystal molecules of the first region are aligned along a plurality offirst alignment directions which forms a plurality of first alignmentangles with respect to a reference direction, and wherein liquid crystalmolecules of the second region are aligned along a plurality of secondalignment directions which forms a plurality of second alignment angleswith respect to the reference direction.
 5. The diffraction grating ofclaim 1, wherein each of the different diffracting zones furthercomprises an alignment layer interposed between the substrate and acorresponding liquid crystal layer, wherein different alignment layersbetween the different liquid crystal layers and the substrate are formedof the same material composition, the different alignment layers causingthe liquid crystal molecules to be aligned differently in the differentdiffracting zones.
 6. The diffraction grating of claim 1, wherein theliquid crystal molecules comprise calamitic liquid crystal moleculesthat are elongated and aligned along an elongation direction.
 7. Thediffraction grating of claim 1, wherein each of the different liquidcrystal layers include a first region and a second region, whereinliquid crystal molecules of the first region are aligned along a firstalignment direction which forms a first alignment angle with respect toa reference direction, and wherein liquid crystal molecules of thesecond region are aligned along a second alignment direction which formsa second alignment angle with respect to the reference direction, thesecond alignment angle different from the first alignment angle.
 8. Thediffraction grating of claim 7, wherein liquid crystal molecules of afirst region of a first liquid crystal layer and liquid crystalmolecules of a corresponding first region of a second liquid crystallayer have substantially the same alignment angle.
 9. The diffractiongrating of claim 8, wherein liquid crystal molecules of a second regionof the first liquid crystal layer and liquid crystal molecules of acorresponding second region of the second liquid crystal layer havedifferent alignment angles.
 10. The diffraction grating of claim 7,wherein liquid crystal molecules of a first region of a first liquidcrystal layer and the liquid crystal molecules of a corresponding firstregion of a second liquid crystal layer have substantially differentalignment angles, and wherein liquid crystal molecules of a secondregion of the first liquid crystal layer and liquid crystal molecules ofa corresponding second region of the second liquid crystal layer havedifferent alignment angles.
 11. The diffraction grating of claim 7,wherein a ratio of lateral widths between the first region and thesecond region is substantially the same between different diffractingzones.
 12. The diffraction grating of claim 7, wherein liquid crystalmolecules of a second region of a first liquid crystal layer and liquidcrystal molecules of a second region of a second liquid crystal layerhave substantially same alignment angles, and wherein a ratio of lateralwidths between the first regions and the second regions is substantiallydifferent between different zones.
 13. The diffraction grating of claim7, wherein liquid crystal molecules of a second region of a first liquidcrystal layer and liquid crystal molecules of a second region of asecond liquid crystal layer have different alignment angles, and whereina ratio of lateral widths between the first regions and the secondregions is substantially different between different zones.
 14. Thediffraction grating of claim 7, wherein the first and second alignmentangles are pre-tilt angles that are measured in a plane perpendicular toa major surface of a substrate and between respective alignmentdirections and the major surface.
 15. The diffraction grating of claim7, wherein the first and second alignment angles are azimuthal anglesthat are measured in a plane parallel to a major surface of a substrateand between respective alignment directions and a reference directionparallel to the major surface.
 16. The diffraction grating of claim 1,wherein the diffraction grating is a transmissive diffraction gratinghaving a transparent substrate.
 17. A head-mounted display deviceconfigured to project light to an eye of a user to display augmentedreality image content, the head-mounted display device comprising: aframe configured to be supported on a head of the user; a displaydisposed on the frame, at least a portion of the display comprising oneor more waveguides, the one or more waveguides being transparent anddisposed at a location in front of the user's eye when the user wearsthe head-mounted display device such that the transparent portiontransmits light from a portion of an environment in front of the user tothe user's eye to provide a view of the portion of the environment infront of the user, the display further comprising one or more lightsources and at least one diffraction grating configured to couple lightfrom the light sources into the one or more waveguides or to couplelight out of the one or more waveguides, wherein the diffraction gratingcomprises the diffraction grating of claim 1.